Fix DNS resolution in containerized environments using ThreadedResolver

[eman]

Problem

DNS resolution failures in containerized environments (Home Assistant, Docker, Kubernetes):

• aiohttp defaults to aiodns resolver when none specified
• aiodns depends on c-ares C binding not reliably available in containers
• Causes errors: aiodns.error.DNSError: (3, 'DNS server returned general failure')
• System tools work fine, but Python async DNS fails

Solution

Use ThreadedResolver explicitly for all aiohttp.ClientSession creations:

• ThreadedResolver uses Python's built-in socket module
• No external c-ares dependency
• Works reliably across all environments

Changes

• src/nwp500/auth.py:
  • NavienAuthClient.__aenter__(): Use ThreadedResolver for session creation
  • NavienAuthClient._ensure_session(): Use ThreadedResolver for backup session
  • refresh_access_token(): Use ThreadedResolver for temporary session

Technical Details

• Minimal changes: 13 lines added, 3 lines removed
• No new dependencies (ThreadedResolver already in aiohttp)
• No breaking changes
• Fully backward compatible

Verification

✓ Linting: All checks passed (ruff format, ruff check)
✓ Syntax: Python compilation successful
✓ Runtime: ThreadedResolver successfully created in all scenarios
✓ No new type errors introduced

Impact

• ✅ Fixes DNS failures in Home Assistant and other containers
• ✅ No performance impact
• ✅ No new dependencies
• ✅ Fully backward compatible

[Copilot]

Pull Request Overview

This PR fixes DNS resolution failures in containerized environments (Home Assistant, Docker, Kubernetes) by explicitly using aiohttp's ThreadedResolver instead of relying on the default aiodns resolver, which depends on the c-ares C binding that may not be available in containers.

Key changes:

• Replace default DNS resolution with ThreadedResolver in all aiohttp.ClientSession creations
• ThreadedResolver uses Python's built-in socket module, eliminating external dependencies
• All three session creation points in auth.py are updated for consistency

[Copilot]

The resolver and connector creation pattern is duplicated in three locations (aenter, _ensure_session, refresh_access_token). Consider extracting this into a helper method like _create_session() to reduce code duplication and make future changes easier to maintain.

[eman]

Update: Code Refactoring Applied ✨

Thanks for the suggestion! I've refactored the code to eliminate duplication:

Changes:

• Added helper method to NavienAuthClient
• Refactored all 3 session creation points to use this single helper
• Eliminates code duplication and improves maintainability

Before (3 duplicate blocks):

resolver = aiohttp.ThreadedResolver()
connector = aiohttp.TCPConnector(resolver=resolver)
self._session = aiohttp.ClientSession(
    connector=connector, timeout=self.timeout
)

After (single source of truth):

def _create_session(self) -> aiohttp.ClientSession:
    """Create session with ThreadedResolver for reliable DNS."""
    resolver = aiohttp.ThreadedResolver()
    connector = aiohttp.TCPConnector(resolver=resolver)
    return aiohttp.ClientSession(connector=connector, timeout=self.timeout)

Updated commit: ca1773c

• Still passes all linting checks
• Maintains same functionality
• Easier to maintain going forward