feat(testing): add async parallel test runner with concurrency + timeout

[Mustafa11300]

Feat: add async parallel test runner for mofa-testing #1598

Problem

The testing crate did not have a dedicated async test execution engine with configurable parallelism and per-test timeout control.
Tests were primarily run through cargo test, and the existing suite runner in runner.rs executes sequentially without configurable concurrency, timeout enforcement, or progress event emission.

Fix

Implemented a new async runner foundation in runner.rs, and exported it from lib.rs.

Key additions:

• AsyncTestRunner with configurable bounded concurrency
• Semaphore-based parallel execution
• Per-test timeout support using Tokio timeout
• Structured progress events:
  • Started
  • Passed
  • Failed
  • Skipped
• Deterministic result collation in input order
• Native integration with existing TestReport and TestReportBuilder
• Support for skipped tests with structured skip metadata

Tests added

Added targeted coverage in async_runner_tests.rs:

• async_runner_collects_pass_fail_and_skipped
• async_runner_respects_concurrency_limit
• async_runner_marks_timeout_as_failed
• async_runner_emits_progress_events
• async_runner_uses_injected_clock_for_report

Verification

Ran:

• cargo test -p mofa-testing

All relevant tests pass.