linux drive selection + linux usb drive benchmark + drive space check

[jamesmarkchan]

summary of changes:

1. Drives dropdown does not display other mounted drives in linux #205
2. usb drives benchmarked on linux are not valid #209
3. Check for enough space to perform benchmark before starting #207

here is a benchmark of a usb drive on ubuntu

[Copilot]

Pull request overview

This PR focuses on improving Linux drive selection and USB-drive benchmarking reliability, addressing issues around drive enumeration, Direct I/O constraints on vfat/FAT32, SMART handling on USB, and pre-flight validation (space/access) before starting a benchmark.

Changes:

• Enumerate Linux drives via /proc/mounts instead of File.listRoots(), and improve drive model display for USB by combining lsblk VENDOR+MODEL.
• Make Direct I/O on Linux more robust by deriving an effective alignment from filesystem block size, and falling back to buffered I/O when Direct I/O fails.
• Add pre-benchmark disk space checks with a safety margin and tighten transaction handling for benchmark persistence.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
jdm-core/src/main/java/jdiskmark/UtilOs.java	Adds Linux mount enumeration and vendor+model lookup; adjusts bus type detection logic.
jdm-core/src/main/java/jdiskmark/Util.java	Switches Linux drive model display to vendor+model.
jdm-core/src/main/java/jdiskmark/SelectDriveFrame.java	Updates static import to the new DriveChecker.
jdm-core/src/main/java/jdiskmark/Sample.java	Introduces Direct I/O retry/fallback behavior and centralizes effective alignment usage.
jdm-core/src/main/java/jdiskmark/Gui.java	Adds early USB SMART gating with user messaging.
jdm-core/src/main/java/jdiskmark/DrivePanel.java	Uses Linux mount enumeration for drive dropdown and improves mount selection logic.
jdm-core/src/main/java/jdiskmark/DriveChecker.java	New helper for target directory validation and disk space pre-checks.
jdm-core/src/main/java/jdiskmark/DriveAccessChecker.java	Removed in favor of DriveChecker.
jdm-core/src/main/java/jdiskmark/BenchmarkWorker.java	Wraps autosave persistence in a try/catch with rollback.
jdm-core/src/main/java/jdiskmark/BenchmarkRunner.java	Adds effective alignment resolution and uses config.testDir for environment mapping.
jdm-core/src/main/java/jdiskmark/Benchmark.java	Hardens deleteAll() transaction handling (rollback on active transaction, rollback on failure).
jdm-core/src/main/java/jdiskmark/App.java	Adds 32K sector alignment option and enforces disk space check before benchmark start.
jdm-core/docs/design.md	Updates documentation reference from DriveAccessChecker to DriveChecker.
jdm-core/docs/benchmarks.md	Adds detailed Linux/USB benchmarking notes (Direct I/O constraints, alignment behavior, SMART, model detection).

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