feat: add use_database() / current_database() API and execute tests in concurrent

[breezewish]

New:

• TiDBClient.current_database
• TiDBClient.use_database

The verbose tests and doc comments are written by AI.

Note: the current implementation is basic, not good, see TODO in the code for the desired state.

[cursor]

Bug: Temporary Client Ownership Causes Resource Conflicts

In TiDBClient.use_database(), a temporary TiDBClient instance (new_client) is created solely to extract its _db_engine and other attributes. This leads to unnecessary object instantiation and a resource ownership issue: new_client retains references to the engine now owned by self. If new_client were to be disposed, it could prematurely dispose of the engine currently in use by the main client, leading to resource conflicts.

pytidb/client.py#L165-L179

pytidb/pytidb/client.py

Lines 165 to 179 in 09fd405

	new_url = self._db_engine.url.set(database=database)
	# Attempt to create the new client first, only dispose and update attributes if successful
	new_client = TiDBClient.connect(
	url=new_url.render_as_string(hide_password=False),
	**self._reconnect_params,
	)
	# Now that new_client is successfully created, dispose the old engine and update all attributes
	self._db_engine.dispose()
	self._db_engine = new_client._db_engine
	self._inspector = new_client._inspector
	self._identifier_preparer = new_client._db_engine.dialect.identifier_preparer
	self._reconnect_params = new_client._reconnect_params

Fix in Cursor • Fix in Web

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