implement stateful connection

[shiyuhang0]

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[pingcap-cla-assistant]

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[Copilot]

Pull request overview

Implements an experimental “stateful connection” mode for the TiDB Cloud Serverless JS driver, enabling session persistence across multiple queries.

Changes:

• Add a Connection.persist() API returning a StatefulConnection wrapper with execute() and close().
• Extend HTTP request handling to send a TiDB-Stateful-Action header to open/close stateful sessions.
• Update integration tests and README documentation; bump package version to 0.3.0.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/version.ts	Bumps internal driver version string to 0.3.0.
src/serverless.ts	Adds TiDB-Stateful-Action header support to POST request helper.
src/index.ts	Introduces persist()/StatefulConnection, adjusts transaction begin flow, and threads stateful action through execute path.
integration-test/basic.test.ts	Adds integration tests for stateful connection open/close behavior.
README.md	Documents stateless vs stateful vs transaction usage; adds notes/constraints.
package.json	Bumps npm package version to 0.3.0.
pnpm-lock.yaml	Adds a pnpm lockfile to the repo.

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