feat(multiset): handle r=ping correctly

[wescopeland]

This PR modifies how game IDs are resolved between the patch and ping routines to ensure consistent behavior when multiset is enabled.

Key changes:

• A new action, ResolveRootGameIdAction, has been added. This action encapsulates game ID resolution logic for both endpoints.
• BuildClientPatchDataAction has been modified to use this action. Tests are unchanged and all remain passing.
• In dorequest.php, ping has been modified to use this action for game ID resolution if multiset is enabled.

A reminder of how game ID resolution works:

• For legacy clients, the loaded hash's direct game ID is used.
• When multiset is disabled, the loaded hash's direct game ID is used.
• When multiset is enabled:
  • For bonus set game hashes, resolve to the core/base game ID.
  • For specialty/exclusive set game hashes, maintain the subset game ID.
  • If the user has globally opted out of subsets, use the loaded hash's direct game ID.

The changes in this PR ensure that:

• The active game ID in ping matches the root-level game ID from patch.
• Legacy clients and users who have opted out of multiset maintain the existing behavior.

It's worth noting the changes in ping are controlled entirely by the VITE_FEATURE_MULTISET feature flag, as clients are already sending both the game ID (g) and the game hash MD5 (x).

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Next steps:

• Handle r=startsession correctly.