Compile schema-specific server binary plans for fast-path binary and packed-binary encoding

[Copilot]

Binary and packed-binary encoding were still using generic runtime tree walks even though the schema fixes most message shapes at load time. This change adds a schema-compiled server fast path that precomputes request/response binary plans and emits packed rows directly for schema-known struct arrays.

• Schema-compiled binary plans

  • Add BinarySchemaPlan to compile per-schema encode/decode plans at binary-encoding construction time.
  • Prebind field/tag ids for schema-known struct, union, and array shapes instead of resolving them through the generic recursive key walker on every message.
  • Keep fallback behavior for shapes that remain dynamic or only partially encodable from schema information.

• Server binary fast path

  • Use compiled plans for server-side request body decode and response body encode.
  • Continue to fall back to the existing generic binary path when no compiled plan applies.
  • Thread the response function name through an internal symbol-keyed header field so response encoding can select the correct result-union plan without affecting the wire format.

• Packed-binary specialization

  • Precompute packed layouts for schema-known arrays of structs.
  • Encode packed rows directly from the source object graph instead of first building the generic binary Map tree and then repacking it.
  • Preserve the existing packer as the safety net for unsupported shapes.

• Binary metadata cleanup

  • Centralize decode-map creation.
  • Export and reuse the packed/undefined sentinels needed by the compiled packer path.
  • Avoid leaking internal response metadata into serialized output.

const binaryEncoding = constructBinaryEncoding(schema);

// Compiled once at schema load:
binaryEncoding.schemaPlan?.encodeResponseBody('fn.getData', {
  Ok_: {
    data: [
      { id: 1, name: 'one' },
      { id: 2, name: 'two' },
    ],
  },
}, true);

This keeps the existing wire contract intact while shifting common server binary work from generic runtime map walking to schema-specific compiled plans.