Implements `pnpm pkg` natively with `get`, `set`, `delete`, and `fix` subcommands.
Workspace usage follows pnpm conventions: use `-r` / `--recursive` for all selected workspace projects, and `--filter` to narrow the selected project graph. This does not add npm-style `--workspace` or `--workspaces` flags.
The PR also extends `@pnpm/object.property-path` with safe set/delete helpers used by the command.
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Co-authored-by: Zoltan Kochan <z@kochan.io>
