Fix AttributeError when pool is None in Bolt3 error handling

[kirill-stepanishin]

Fix AttributeError when pool is None in Bolt3 error handling

Problem

When a Neo4jError is raised in Bolt3 connections, the error handler attempts to call self.pool.on_neo4j_error() without checking if self.pool exists. This causes an AttributeError when the connection pool is None or not available.

Solution

Added a null check for self.pool before calling on_neo4j_error(), consistent with the existing error handling pattern used for ServiceUnavailable, DatabaseUnavailable, NotALeader, and ForbiddenOnReadOnlyDatabase exceptions in the same method.

Changes

• src/neo4j/_async/io/_bolt3.py: Added if self.pool: check before await self.pool.on_neo4j_error()
• src/neo4j/_sync/io/_bolt3.py: Auto-generated sync version with the same fix

This prevents crashes when handling Neo4j errors in scenarios where the connection pool is not initialized or has been cleared.

Note:
I am a first-time contributor and have just signed the CLA