Fix branch latest update on explicit remote sync

[piyushbag]

Summary

Fixes branch latest pointer maintenance when lore sync <revision> --remote targets an explicit revision.

• Propagate search_location into location for explicit revision sync so remote sync updates branch latest.
• Use the post-sync branch (synced_branch) instead of the pre-sync branch when calling store_latest.

Fixes #122

Test plan

• cargo +nightly fmt --all
• cargo clippy -p lore-revision --all-targets -- -D warnings --no-deps
• cargo test -p lore-revision sync_explicit_revision

Evidence

$ cargo test -p lore-revision sync_explicit_revision
running 1 test
test tests::sync_explicit_revision ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured

The test seeds a stale branch latest, syncs forward with --remote, and asserts the latest pointer matches the synced revision.