[SunSi12138]

Summary

Implements #747 as a production generated/runtime path rather than a benchmark-only shadow implementation.

• generate readonly struct Core implementations for native generated DTO / union / collection / request Codecs
• extract Core once from the authoritative provider-owned class Codec and retain it in generated proxies/stubs
• preserve statically known Codec types through generated client request, unary response, client-stream, server-stream, duplex, retry, telemetry, and interceptor paths
• add closed-generic RpcRequestOperation<T,TCodec> and PooledAsyncStreamDispatcher<T,TCodec> pooling paths
• preserve static Core through generated server inbound/outbound stream bridges and client stream sinks
• keep adapter/custom/dynamic Codec routes on the existing interface fallback
• bump the exact generated ABI identity and update public API/release/migration assets
• add focused generator/runtime tests plus a production-generated static Core evidence executable that is built by the solution

Pre-PR self-review 1 — compile / low-level correctness

Completed on the final pre-PR head.

• checked all changed C# files for conflict markers / TODO placeholders and basic declaration consistency
• verified new partial declarations match existing partial owners
• verified every added public generated bridge has a concrete SharpLink implementation, so production generated calls do not accidentally fall through a default interface implementation
• verified Runtime and Generator ABI identities match exactly
• verified the public API baseline includes all added bridge members
• verified the frozen API4 binary remains intentionally stale and is still rejected by exact ABI identity
• found and fixed one concrete pre-PR issue: SharpLink.StaticCodecCoreEvidence was an Exe without an entry point and was outside Sharplink.slnx; it now has a manifest-validating Program and is built by the solution
• local dotnet execution is unavailable in this environment, so GitHub CI is the authoritative compiler/test validation

Pre-PR self-review 2 — #747 acceptance mapping

• production Generator emits readonly struct Core: implemented
• DTO / union / collection / generated request Core: implemented
• provider/class Codec remains authoritative owner: Core is extracted from the provider-resolved class instance; no second graph/global singleton
• perf: preserve concrete codec types in generated code #727 concrete binding information is reused for generated child Codec fields
• Proxy and Stub retain static Core where the generated implementation is statically nameable
• all five RPC shapes route through generated Codec-preserving bridges
• client request encode preserves concrete Core
• unary/client-streaming response decode uses closed-generic RpcRequestOperation<T,TCodec>
• client stream send / server stream send / inbound stream dispatch preserve Codec type
• dispatcher uses closed-generic PooledAsyncStreamDispatcher<T,TCodec>
• adapter/custom/dynamic stream routes remain on interface fallback; no runtime existential opener/visitor is introduced
• exact-size static stream path releases snapshots exactly once through the existing sized-send ownership machinery
• ABI identity/public API/migration assets are updated
• generator coverage explicitly asserts all five RPC shapes and dynamic fallback
• runtime coverage exercises operation pool reuse, dispatcher pool reuse, payload-less response validation, and exact-size snapshot release

Validation

Draft CI is the executable validation path. The PR remains draft until the current head passes the repository's required checks and any CI-discovered compile/test issues are fixed.

Performance/NativeAOT evidence remains a merge gate per #747; this PR does not treat synthetic pre-#747 evidence as a substitute for production generated/runtime measurements.

Fixes #747