feat(powerbi): add configurable request timeouts and async timeout handling to PowerBIDataset

[MANYA12-STAR]

Description

This PR adds first-class support for configurable request timeouts in PowerBIDataset for both synchronous (run) and asynchronous (arun) execution paths.

Key improvements:

• Introduced a new request_timeout field on PowerBIDataset, enabling instance-level timeout configuration.
• Added input validation to prevent invalid timeout values.
• Updated run() and arun() to use explicit timeouts when provided, or fall back to the instance default.
• Implemented async timeout handling using aiohttp.ClientTimeout.
• Added a complete unit test suite (test_powerbi_timeout.py) covering:
  • default timeout behaviour
  • explicit timeout overrides
  • async behaviour with internal/external sessions
  • invalid timeout values
• Ensures fully backward-compatible behavior.

Issue

Fixes #332 — Add configurable timeout support and improve reliability of PowerBI utilities.

Dependencies

No new dependencies added.
All existing optional dependencies remain optional.