feat(daemon,transfer): consume fake super = yes module directive (#1904)

[oferchen]

Summary

• Threads the daemon module directive fake super = yes from ModuleConfig.fake_super through ServerConfig.fake_super and into MetadataOptions.fake_super, so daemon-side receivers honour the directive end-to-end.
• Previously, fake super = yes was parsed but never consumed: receivers issued real chown() calls regardless of the directive, which silently dropped ownership for non-root daemons and contradicted upstream's clientserver.c:1106-1107 semantics.
• Adds an end-to-end daemon push test that pushes with -og to a module configured with fake super = yes and asserts the destination carries the user.rsync.%stat xattr.

Wire-up path

ModuleConfig.fake_super (already parsed)
  -> ServerConfig.fake_super              [transfer/config]
    -> MetadataOptions.fake_super         [transfer/receiver/transfer.rs]
      -> apply_ownership_via_fake_super   [metadata/apply/ownership.rs] (already in place)
        -> store user.rsync.%stat xattr   [metadata/fake_super.rs] (already in place)

Files changed

• crates/transfer/src/config/mod.rs (+23): add pub fake_super: bool field with upstream-cited rustdoc.
• crates/transfer/src/config/builder.rs (+23): add .fake_super(bool) builder method.
• crates/transfer/src/config/builder_tests.rs (+21): default-false assertion and round-trip test.
• crates/daemon/src/daemon/sections/module_access/client_args.rs (+7): set cfg.fake_super = module.fake_super in build_server_config.
• crates/transfer/src/receiver/transfer.rs (+6/-1): chain .fake_super(self.config.fake_super) on the receiver's MetadataOptions::new() builder.
• crates/daemon/src/tests/chunks/daemon_fake_super_module_push.rs (+158, new): end-to-end daemon test.
• crates/daemon/src/tests.rs (+2): wire the new chunk into the test harness.

Upstream references

• clientserver.c:1106-1107 — daemon fake super = yes demotes the receiver's am_root and forces fake-super semantics regardless of client args.
• loadparm.c — fake super module parameter parsing.
• rsync.c:set_file_attrs() — fake-super stores ownership in xattrs.
• xattrs.c:set_stat_xattr() — user.rsync.%stat encoding format.

Per upstream, client --fake-super is demoted to --super on the wire before reaching the daemon, so the directive is purely daemon-config-driven; we do not parse --fake-super server-side.

Test plan

• crates/daemon/src/tests/chunks/daemon_fake_super_module_push.rs covers the end-to-end daemon push case (skips gracefully on filesystems without user.* xattr support).
• crates/transfer/src/config/builder_tests.rs::fake_super_round_trips_through_builder covers the builder.
• crates/transfer/src/config/builder_tests.rs::default_optional_fields adds the default-false assertion.
• Existing crates/daemon/src/rsyncd_config/tests.rs::module_fake_super_yes_parses_to_true_for_am_root_demotion covers the parser side (unchanged).
• CI: fmt+clippy, nextest stable, Windows stable, macOS stable, Linux musl stable.

Closes #1904.