Fix git-lfs file smudging in zone source accessors

[vwassan]

Fix git-lfs file smudging in zone source accessors

Problem

Zone source accessors (getZoneStorePath, mountZoneByTreeSha, getZoneFromCheckout) were created with smudgeLfs = false, causing git-lfs pointer files to be copied into the Nix store as-is instead of being fetched and replaced with their real content. This broke builds for zones containing LFS-tracked files (e.g. //areas/platforms/query-engine), with errors like:
internal/gen/catalog/generated_schema_shopify.go:1:1: expected 'package', found version

The root cause is two-fold:

• smudgeLfs was never enabled for zone accessors
• Even if enabled, zone accessors are created from tree SHAs, but lfs::Fetch::shouldFetch() uses GIT_ATTR_CHECK_INCLUDE_COMMIT which requires a commit OID to resolve .gitattributes — so LFS attribute lookup would silently fail regardless

Solution

• Add lfsCommitRev to GitAccessorOptions — when set, this commit hash is passed to lfs::Fetch instead of the tree hash, allowing correct .gitattributes lookup when the accessor is created from a tree SHA
• Enable smudgeLfs = true on all three zone accessor call sites, passing the world commit hash (from --tectonix-git-sha) via lfsCommitRev

Note: getWorldGitAccessor() is intentionally left with smudgeLfs = false — it is only used for path validation and tree SHA computation, not for copying content into the store.

Files Changed

• src/libfetchers/include/nix/fetchers/git-utils.hh — add lfsCommitRev to GitAccessorOptions
• src/libfetchers/git-utils.cc — use lfsCommitRev in lfs::Fetch constructor; include in makeFingerprint
• src/libexpr/eval.cc — enable smudgeLfs = true + lfsCommitRev on all zone accessor call sites

[vwassan]