Optimization: shared session init

[kevinbouge]

Fixes

1. Shared Session Initialization: Added a single, persistent Soup.Session instance (this._httpSession) in the constructor of AirAwareApplet. This ensures connection pooling (HTTP Keep-Alive) is reused across multiple refreshes, reducing connection latency and memory allocation overhead.
2. Proper Cleanup: Handled cleanup by calling this._httpSession.abort() inside the _destroy() method of applet.js. This guarantees that if the applet is removed or reloaded, any active requests on the session are immediately aborted, preventing memory leaks or orphaned callbacks.
3. Session Propagation: Updated the calls to all asynchronous providers (Open-Meteo Air Quality, Open-Meteo Weather, OpenStreetMap Vegetation, and Nominatim Reverse Geocoder) to pass the shared this._httpSession instead of letting them instantiate their own temporary sessions.

Tested
./validate-spice airaware@kevinbouge
./test-spice airaware@kevinbouge
./cinnamon-spices-makepot airaware@kevinbouge
airaware@kevinbouge/tests/run-tests.sh
Local Cinnamon panel testing