Add async runtime and concurrent vault support

[AronAxe]

Summary

• add an executor-backed AsyncRuntime façade while preserving the synchronous API
• propagate task and thread-safe token cancellation and kill/reap RTK subprocesses
• enable SQLite WAL concurrency and stress-test multi-thread/process deduplication, integrity, and lease claims
• document async usage, streaming boundaries, cancellation semantics, and local-vault concurrency

Verification

• 141 passed, 2 skipped
• ruff check and format check pass
• structural benchmark unchanged at 82.8% aggregate token reduction
• wheel/sdist build, twine check, release verification, and wheel module inspection pass
• independent Gemini 3.1 Pro review completed; actionable findings addressed

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Update the install pin before advertising async imports

When a user follows the immediately preceding adapter installation command, pip installs commit e02a035d52cc2b0e6e95748b35deb1f61656a4a3, whose package tree contains neither async_runtime.py nor these exports from rtk_hermes_plus.__init__. The documented import therefore raises ImportError for exactly the users this new section targets; update the installation reference to a revision containing the async API, or clearly require an unreleased/current checkout.

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