command: Respect smart sync override declaratively by default

Introduce a `RESPECT_SMART_SYNC_OVERRIDE` class attribute to the base
`Command` class, defaulting to `True`. This allows subcommands to
automatically respect the smart sync override manifest if it exists.

The override is applied in `CommonValidateOptions` before any
subcommand-specific validation or execution occurs. The `sync` and
`init` commands explicitly opt out.

This ensures all workspace-aware subcommands consistently align with the
active smart sync override manifest. It also fixes a bug in
multi-manifest setups where running a command from a submanifest would
not apply the override to the outer manifest, causing inconsistency when
resolving projects across all manifests.

Bug: 279204331
Change-Id: I9426e90a13a77ce6bd94b4a82efda4d485cbe116
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/585081
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

subcmds/init.py

@@ -33,6 +33,7 @@ _REPO_ALLOW_SHALLOW = os.environ.get("REPO_ALLOW_SHALLOW")
 
 class Init(InteractiveCommand, MirrorSafeCommand):
     COMMON = True
+    RESPECT_SMART_SYNC_OVERRIDE = False
     MULTI_MANIFEST_SUPPORT = True
     helpSummary = "Initialize a repo client checkout in the current directory"
     helpUsage = """