Port gRPC retry service-config validation

Bun corpus source

• js/third_party/grpc-js/test-retry-config.test.ts
• sequential corpus position: 3989

Scope

• expose executable validateServiceConfig behavior through the gRPC bootstrap
• validate retry, hedging, and retry-throttling policy fields and status codes
• preserve upstream-compatible validation messages
• attach stable error codes, policy paths, causes, and operation/source frames to rejected configurations
• add focused and permanent regression coverage

Tracking: #66

Implemented and published in 99efb34e7 (feat(third-party): port gRPC retry validation).

What landed:

• executable validateServiceConfig support for retry, hedging, and retry-throttling policies
• validation for attempts, backoff durations, multipliers, token limits/ratios, and numeric/named status codes
• upstream-compatible rejection messages across all copied Bun cases
• structured ERR_GRPC_SERVICE_CONFIG failures with policy, path, preserved cause, and ServiceConfig.validateServiceConfig operation/source stack frames
• separate validation and legacy parse-error constructors, preventing helper shadowing and retaining existing ERR_INVALID_ARG_VALUE behavior
• TypeScript lowering for the copied retry-config test and permanent third-party coverage

Verification:

• exact Bun file: 28 passed, 0 failed, 0 todo, 0 unsupported
• affected gRPC positions 3985–3989: 98 passed, 4 upstream todos, 0 failed, 0 unsupported
• permanent gRPC diagnostics: 16 passed
• permanent SQL adapter and third-party mini-suite gates: passed
• zig fmt --check packages/home_test/src/corpus_runner.zig: passed
• git diff --check: passed

Sequential corpus ledger through position 3989: 331 executable files, 2,791 passed, 213 upstream todos, 0 failed, 0 unsupported, 171 intentionally allowed-empty files.

Tracking: #66