fix(pnpm): write pnpmOverrides to pnpm-workspace.yaml

[unstubbable]

The fix command reads overrides from pnpm-workspace.yaml but never writes the corrected versions back, so any mismatch that lint flagged was reported as fixed (✓) while the file was actually left untouched.

The read side was added in 72ce5ef, which pointed the default pnpmOverrides dependency type at pnpm-workspace.yaml with source: PnpmWorkspace. The matching write path in copy_expected_specifier_yaml was never extended, though: it returns early for any instance without a catalog name, so the versionsByName workspace instances (i.e. overrides) fall through and nothing is written.

An overrides block is a flat name: version map with the same shape as the default catalog: block, so the single-block logic now lives in reusable build_block_insert_patch and ensure_yaml_block helpers, extracted from build_insert_patch and ensure_catalog_block (which the default catalog delegates to). Non-catalog versionsByName workspace instances route through a new insert_into_yaml_block, the single-block sibling of insert_catalog_definition. The block key comes from the dependency type's path (e.g. /overrides), so the same path also covers any user customType with source: PnpmWorkspace.

Reads and lints already detected these mismatches, so apart from the now-working write path the behaviour is unchanged. A new regression test, pnpm_fix_updates_overrides_in_yaml, asserts the override is rewritten in pnpm-workspace.yaml and the file is marked dirty.

Tip

Best reviewed with hidden whitespace changes because of the shared helper extraction.

[JamieMason]

Damn, nice catch. I checked that catalogs were written back to this file, but I must've totally overlooked overrides, thanks a lot.