feat(rsc): expose callable argument metadata

[hi-ogawa]

• part of Support Framework-Owned "use cache" Server Functions #1336
• closes Exclude Undeclared Caller Arguments From "use cache" Cache Keys #1392
• related to Omit unused args when calling "use cache" functions vercel/next.js#72506
• closes feat(rsc): expose server function metadata #1258 (supersedes)

Framework-owned callable wrappers cannot recover source parameter admission or generated closure capture boundaries from Function.length. This matters when framework-supplied arguments should not affect fixed-signature cache keys while declared arguments and decoded captures should.

This PR exposes { count, hasRest } for statically known source functions and boundArgumentCount for inline directive lowering. The bound count describes the generated call shape, so direct captures occupy their actual number of slots while encoded captures occupy one. The callable cache example consumes this metadata and demonstrates fixed-prefix admission, rest pass-through, and decoded capture identity in development and production.

[hi-ogawa]

Closing since this should split to

• Exclude Undeclared Caller Arguments From "use cache" Cache Keys #1392
• Support use cache with closure encryption #1393