feat(git): add --rename-threshold option to DiffviewOpen and DiffviewFileHistory (#301)

[dlyongemallo]

Closes #301.

[Copilot]

Pull request overview

This PR adds a --rename-threshold={n} CLI option to :DiffviewOpen and :DiffviewFileHistory, letting users override the global rename_threshold config on a per-view basis for git's rename detection (-M<n>%). I traced the full data flow end-to-end for both entry points and it is wired correctly and backward compatible (the new value always falls back to the global config when absent).

Changes:

• Adds parse_rename_threshold_flag (git adapter) that validates the flag via the shared config.validate.integer helper (accepts 40/40%, range 0–100, warns and falls back on invalid input), wires it into diffview_options/file_history_options, and threads it through tracked_files and stream_fh_data; registers completion.
• Forwards the value per-view via DiffViewOptions.rename_threshold → LayoutOpt.rename_threshold → tracked_files, and via GitLogOptions.rename_threshold → file-history stream.
• Emits a warning for Jujutsu (unsupported), exports config.validate, and documents the option; adds functional tests.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lua/diffview/vcs/adapters/git/init.lua	Parses/validates the flag and applies -M<n>% in file-listing and history paths; adds completion.
lua/diffview/vcs/utils.lua	Forwards dv_opt.rename_threshold into the per-view opt for tracked_files.
lua/diffview/vcs/adapter.lua	Adds rename_threshold to LayoutOpt type.
lua/diffview/scene/views/diff/diff_view.lua	Adds rename_threshold to DiffViewOptions type.
lua/diffview/config.lua	Adds rename_threshold to git log-option schema/defaults; exports validate.
lua/diffview/vcs/adapters/jj/init.lua	Warns that the option is unsupported for Jujutsu.
lua/diffview/tests/functional/git_adapter_spec.lua	Tests parsing for open and file-history options.
doc/diffview.txt	Documents the new option for both commands.

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