smartcontract: add AdminGroupBits ResourceExtension (#3343)

[Rhovian]

Summary of Changes

This PR adds AdminGroupBits as a new ResourceExtension type, including PDA derivation, seed wiring, range definition (0..32), and focused allocator/resource-extension tests for lowest-available allocation and exhaustion.

Assumptions for follow-up work:

• This PR does not change global bootstrap or SDK/CLI SetGlobalConfig account lists, so AdminGroupBits is expected to be created explicitly by the future RFC-18 LinkColorInfo flow.
• The “bits are never reused after deletion” policy is also deferred to that consumer logic by not calling deallocate_id() when a color is removed, rather than changing the generic IdAllocator behavior.

Testing Verification

cc @ben-malbeclabs