feat(git): replace isomorphic-git with Effect Git - W-22711959

[mshanemc]

What does this PR do?

• Replace isomorphic-git with an Effect-native Git implementation while keeping the shadow repository at .sf/orgs/<orgId>/localSourceTracking.
• Replace the ShadowRepo class with a factory and cached, stream-derived added / modified / deleted status; use recordSync for advancing the local baseline.
• Preserve symlink targets and modes, atomically replace the index, and serialize commit ancestry under the index lock.
• Migrate the existing worktree changes, including remote tracking and type/name resolution improvements, onto current main dependencies.

Known limitation: stale-lock cleanup is mtime-based (five minutes by default); a competing writer could treat an unusually long live lock as stale.

Validation: yarn build, yarn test, yarn check:effect, and yarn check:circular-deps.

What issues does this PR fix or reference?

forcedotcom/salesforcedx-vscode#7174, forcedotcom/salesforcedx-vscode#7278, @W-22711959@