feat: add gas estimates rpc and spn-bidding crate

[Farhad-Shabani]

What

Two pieces that let bidders size proof requests by expected gas instead of declared limits:

GetProgramGasEstimates RPC. Batch lookup of per-program gas estimates, derived from fulfilled request history. The estimation method lives server-side and can change without touching this contract; programs with no history are simply absent from the response. Server caps the batch size per call.

spn-bidding crate. Pure, dependency-free bidding policy shared by consumer repos.

• gas-aware admission: solo-feasibility and loaded-schedulability checks against a request's effective deadline, including wrap-stage capacity packing
• expected-gas policy: published estimate scaled by an operator multiplier, capped by the request's own limits
• client-side TTL cache for estimate resolutions
• port the performance-requirement deadline math

Why

Bidders previously admitted work on concurrency counts alone, so clusters over- or under-committed depending on the proof mix. Publishing estimates from the network and centralizing the policy math gives every prover the same admission foundation, with one home for the logic instead of per-bidder copies.