fix(alist_v3): set child paths so nested directories resolve

[Elity]

Summary / 摘要

AListV3.List never set Path on the objects it returns. op.Get resolves a
child by handing back the object from its parent's listing verbatim, so that
object is what the next List receives as dir — and with an empty Path, the
driver asked the upstream server for "".

An OpenList/AList server resolves an empty path to its own root, so the request
did not fail; it returned the wrong directory. Every level below the mount point
served the upstream root back, producing an endless self-similar directory: you
click into a folder, get the same listing again, and the breadcrumb grows one
segment each time.

User-visible behavior change:

• Subdirectories of an AList V3 mount now open correctly. Previously only the
  mount root worked, because op.Get builds the root object itself from
  IRootPath and that one does carry a Path.

Implementation change:

• List now sets Path: path.Join(dir.GetPath(), f.Name) on each returned
  object, which is what drivers/openlist already does
  (drivers/openlist/driver.go:98).

This is a regression from 96cd7143 — refactor(op): remove automatic Path
assignment (#1734). That commit removed the block in op.List that used to
fill in a child's Path:

- if s, ok := f.(model.SetPath); ok && f.GetPath() == "" && dir.GetPath() != "" {
-     s.SetPath(stdpath.Join(dir.GetPath(), f.GetName()))

on the stated grounds that "Path和Id只在驱动内使用，不应由op.List设置Path", and
migrated the affected drivers to set it themselves. drivers/alist_v3 was
missed in that migration; drivers/openlist, which is otherwise a near-identical
file, was not.

Scope notes:

• ListArchive also returns objects without a Path, but drivers/openlist
  behaves identically there, so it is left untouched.
• drivers/alist_v3 lacks PassRefreshFlagToUpsteam. That is a feature
  difference, not part of this defect.

No configuration, storage format, API or migration behavior is affected.

• This PR has breaking changes.
  / 此 PR 包含破坏性变更。
• This PR changes public API, config, storage format, or migration behavior.
  / 此 PR 修改了公开 API、配置、存储格式或迁移行为。
• This PR requires corresponding changes in related repositories.
  / 此 PR 需要关联仓库同步修改。

Related repository PRs / 关联仓库 PR:

• OpenList-Frontend: N/A
• OpenList-Docs: N/A

Related Issues / 关联 Issue

Fixes #2077 — reported as "点击任意子目录继续进入时，发现会出现套娃". That issue was
closed after the reporter switched to the OpenList driver, but the AList V3
driver bug itself was never fixed.

cc @xrgzs — you triaged #2077 and noted that this driver is a copy kept for
newer AList API compatibility, so you are probably the right person to check
that aligning it with drivers/openlist here is the intended direction.

Testing / 测试

• go test ./...
• Manual test / 手动测试:

go test ./... is not checked because it does not pass on main in this
environment, for reasons unrelated to this change:

• go vet's printf analyzer, which go test runs by default, fails the build
  of drivers/123, drivers/189, drivers/189pc, drivers/chaoxing,
  drivers/google_drive, drivers/google_photo, drivers/lanzou and three
  internal/offline_download/* packages with non-constant format string.
• drivers/onedrive_sharelink.TestNoRedirectClientUsesSharedSettings panics
  with a nil pointer dereference at internal/net/serve.go:289, because
  conf.Conf is nil outside a booted server.

What was run instead:

go build ./...
go vet ./drivers/alist_v3/...
gofmt -l drivers/alist_v3/
go test -race -count=1 ./drivers/alist_v3/...

Manual test: an OpenList v4 instance mounting another OpenList v4 instance over
AList V3. Before the fix, every directory below the mount point returned the
upstream server's root. After the fix, a 384-entry directory and its children
list correctly, three levels deep.

Two tests are added in drivers/alist_v3/driver_test.go:

• TestListSetsChildPaths — every returned object carries
  path.Join(dir.GetPath(), name).
• TestListDoesNotLoopOnNestedDirectories — descends three levels, feeding each
  listing's object back into List the way op.Get does, and asserts both the
  listings and the exact paths the upstream server was asked for.

The fake upstream deliberately falls back to its own root for an unknown path
instead of returning 404, because that is what a real server does. Answering 404
would turn the defect into a loud error and the loop would not reproduce.

Both tests fail on main:

--- FAIL: TestListSetsChildPaths
    child "concerts" has path "", want "/drive/concerts"
--- FAIL: TestListDoesNotLoopOnNestedDirectories
    listing under "/drive/concerts" is [drive public], want [live-in-tokyo]

Mutation-checked: Path: f.Name, Path: dir.GetPath() and Path: "" are each
caught by the tests.

The new tests install their own resty client rather than calling
base.InitClient(), to avoid the same nil conf.Conf dereference that makes
drivers/onedrive_sharelink panic.

Checklist / 检查清单

• I have read CONTRIBUTING.
  / 我已阅读 CONTRIBUTING。
• I confirm this contribution follows the repository license, contribution policy, and code of conduct.
  / 我确认此贡献符合仓库许可证、贡献规范和行为准则。
• I have formatted the changed code with gofmt, go fmt, or prettier where applicable.
  / 我已按适用情况使用 gofmt、go fmt 或 prettier 格式化变更代码。
• I have requested review from relevant maintainers or code owners where applicable.
  / 我已在适用情况下请求相关维护者或代码所有者审查。

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  / 此 PR 包含 AI 辅助内容。

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[xrgzs]

I suggest reducing the test code from 173 lines to around 20–50 lines, or just remove it. There’s no need to introduce an entire fake server just to cover a single line of production code.

[Elity]

Cut to a single test: 65 lines, 46 of them code. Dropped the second test, the recorder type and the helper funcs, and inlined the driver setup.

I kept the httptest server rather than removing the file. List does its work over HTTP, so there is no seam to exercise it without a server — the alternative here is no test at all. The fake upstream falls back to its own root for unknown paths, which is what makes the loop reproduce; without the one-line fix it fails with:

child of "/drive" has path "", want "/drive/concerts"

Happy to drop the file entirely if you would rather this package stay test-free.