fix(storage): adapt checkpoint lock test helpers to fs4 1.x

[DecisionNerd]

Summary

• Replace bare FileExt::try_lock_* / unlock in checkpoint contention test helpers with crate::file_lock bool-shaped wrappers
• Unblocks CI Gate after the fs4 1.1.0 bump (chore(deps): bump fs4 from 0.13.1 to 1.1.0 #465) broke helpers added in fix(storage): close recovery WriterBusy window on checkpoints.lock #469

Test plan

• cargo test -p graphforge-storage --lib project_checkpoints::tests:: (35 passed, 1 ignored)
• CI Gate green on this head

Fixes #480

Made with Cursor

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📥 Commits

Reviewing files that changed from the base of the PR and between 9dbfed8 and 8d679e6.

📒 Files selected for processing (2)

• crates/graphforge-api/src/repository.rs
• crates/graphforge-storage/src/project_checkpoints.rs

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