This PR removes the timezonefinder dependency that was automatically looking up timezones based on latitude/longitude coordinates in the Location class.

Problem

The timezonefinder dependency alone is 50M+ in size and depends on numpy (another 16M+), resulting in a total bloat of 66M+ for a feature with no known users. This large dependency size also prevents pre-built binaries from being available for ARM platforms.

Solution

• Removed dependency: Removed timezonefinder >= 6.2.0, < 7 from pyproject.toml
• Simplified behavior: Location.timezone now remains None unless explicitly provided during construction
• Removed automatic lookup: Eliminated the __post_init__ method that performed timezone lookup from coordinates
• Updated tests: Removed timezone finder mocking and updated tests to verify the new behavior
• Added documentation: Comprehensive RELEASE_NOTES.md with migration guide

Breaking Change

This is a breaking change shipped in a patch release because this feature has no known users. The timezone lookup is no longer performed automatically.

Migration for Users Who Need Timezone Lookup

If timezone lookup from coordinates is needed, install timezonefinder separately and implement manual lookup:

# Install: pip install timezonefinder
from timezonefinder import TimezoneFinder
from zoneinfo import ZoneInfo
from frequenz.client.microgrid import Location

tf = TimezoneFinder()
tz_name = tf.timezone_at(lat=52.52, lng=13.405)
timezone = ZoneInfo(tz_name) if tz_name else None
location = Location(latitude=52.52, longitude=13.405, timezone=timezone)

Before/After

Before:

# Automatic timezone lookup
location = Location(latitude=52.52, longitude=13.405)
print(location.timezone)  # ZoneInfo('Europe/Berlin') - looked up automatically

After:

# Explicit timezone only
location = Location(latitude=52.52, longitude=13.405)
print(location.timezone)  # None - no automatic lookup

# Or provide explicitly
location = Location(latitude=52.52, longitude=13.405, timezone=ZoneInfo('Europe/Berlin'))
print(location.timezone)  # ZoneInfo('Europe/Berlin')

Fixes #75.