fix(core): read git 2.55's quoted -L paths and keep the partial-clone hint

[RutaTang]

Summary

Two clew-core git tests have been red on main since the GitHub runners moved to git 2.55.0 (both the Linux and macOS test jobs). Both are the product's, reproduced with a local build of git 2.55.0 and fixed in crates/clew-core/src/git.rs:

• log -L paths are quoted now. git 2.55 prints historical paths in the standard C-quoted form, and a name containing a space ends its ---/+++ label with a tab (git's diff.c), which the header decoder did not strip. The quoted name then failed to unquote, the record was undecodable, and that step vanished from a symbol's history (a_newline_in_a_historical_path_neither_splits_nor_relabels_records). standard_header_path now drops the trailing tab before unquoting; a name never ends in one itself, since a raw tab is always quoted.

• The partial-clone hint keyed on git's wording. It looked for "could not fetch <oid> from promisor remote", which 2.55 no longer prints for a cat-file (it says "bad file", as for a corrupt repository; show, log -L and rev-parse moved to their own words). The runner now decides: when a command fails over a missing object (names_a_missing_object), it asks the repository whether it names a promisor remote (remote.<name>.promisor or extensions.partialClone), and GitError::Failed carries the answer in a new partial_clone field. A corrupt repository is not called a partial clone, and the probe runs only on such failures, so the normal path spawns nothing extra (a_partial_clone_never_fetches_through_its_remote).

No fetch was ever attempted under 2.55 either (GIT_NO_LAZY_FETCH still holds); only the message had lost its explanation.

Tests

• The decoder test gains the tabbed labels, quoted and unquoted.
• A unit test pins the hint's rule: the field earns it, the old "promisor remote" wording still does, a bare "bad file" does not.

Verification

Check	Result
git:: tests under git 2.55.0 (local build)	39 passed
git:: tests under git 2.43.0	39 passed
scripts/hermetic-test.sh for core, server, protocol under git 2.55.0	809 passed, 0 failed
cargo clippy --all-targets -- -D warnings (core, server)	0 warnings
cargo doc --document-private-items with -D warnings (core, server)	passes
cargo fmt --all -- --check	passes

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