Add ThreadPoolExecutor unit test inventory

[enricopiovesan]

Summary

• Rename the existing ThreadPoolExecutor inline tests to the exact Unit test suite: ThreadPoolExecutor (spec 047) #506 inventory names.
• Add concurrency, panic recovery, thread-safety, and drop/lifecycle unit coverage.
• Keep the change scoped to crates/traverse-runtime/src/executor/thread_pool.rs test code only.

Governing Spec

• 001-foundation-v0-1
• 002-capability-contracts
• 003-event-contracts
• 004-spec-alignment-gate
• 005-capability-registry
• 006-runtime-request-execution
• 007-workflow-registry-traversal
• 008-expedition-example-domain
• 009-expedition-example-artifacts
• 010-runtime-state-machine
• 013-browser-runtime-subscription
• 011-event-registry
• 018-event-driven-composition
• 019-downstream-consumer-contract
• 017-ai-agent-packaging
• 023-browser-hosted-mcp-consumer-model
• 024-placement-constraint-evaluator
• 025-wasm-executor-adapter
• 012-execution-trace-tiered
• 026-event-broker
• 014-service-type-taxonomy
• 015-capability-discovery-mcp
• 016-runtime-placement-router
• 027-expedition-wasm-port
• 028-schema-alignment-gate-v02
• 029-integrated-observability
• 030-security-identity-model
• 031-supply-chain-hardening
• 032-universal-data-access
• 033-http-json-api
• 034-programmatic-registration
• 035-multi-agent-isolation
• 036-event-subscription-replay
• 037-semver-range-resolution
• 038-wasi-host-insulation
• 039-connector-plugin-architecture
• 040-contractual-enforcement-gate
• 041-workflow-composition-api
• 042-mcp-library-surface
• 043-module-dependency-management
• 044-application-bundle-manifest
• 045-governed-model-dependency-resolution
• 046-public-cli-app-registration
• 047-thread-pool-executor
• 048-semver-publishing-pipeline
• 049-v1-milestone-gate

Project Item

• Closes Unit test suite: ThreadPoolExecutor (spec 047) #506
• Project 1 item: PVTI_lADOEbiBt84Bbyp1zgxqu_4

Validation

• cargo test -p traverse-runtime thread_pool
• rg '^\\s*fn (config_capacity_zero_returns_error|config_capacity_max_valid|config_capacity_over_max_returns_error|config_capacity_one_valid|execute_native_returns_correct_output|execute_native_error_propagates|execute_wasm_artifact_type_returns_unsupported|concurrent_calls_run_in_parallel|pool_size_one_serialises_calls|independent_calls_do_not_share_state|panicking_handler_returns_execution_failed|pool_usable_after_panic|multiple_sequential_panics_do_not_exhaust_pool|executor_is_send_sync|arc_wrapped_executor_callable_from_multiple_threads|executor_drops_cleanly_after_use|executor_drops_cleanly_with_no_calls)\\b' crates/traverse-runtime/src/executor/thread_pool.rs
• rg 'unwrap\\(|expect\\(|panic!|sleep\\(Duration::from_millis\\(([5-9][0-9][0-9]|[1-9][0-9]{3,})\\)' crates/traverse-runtime/src/executor/thread_pool.rs
• cargo clippy --all-targets -- -D warnings
• cargo test -p traverse-runtime
• bash scripts/ci/repository_checks.sh
• git diff --check
• PATH="$HOME/.cargo/bin:$PATH" LLVM_COV=/Users/enricopiovesan/.rustup/toolchains/1.94.0-aarch64-apple-darwin/lib/rustlib/aarch64-apple-darwin/bin/llvm-cov LLVM_PROFDATA=/Users/enricopiovesan/.rustup/toolchains/1.94.0-aarch64-apple-darwin/lib/rustlib/aarch64-apple-darwin/bin/llvm-profdata bash scripts/ci/coverage_gate.sh