Add missing Python datasource bindings

[josephbirkner]

Fixes #64.

Summary:

• Exposes LocateRequest/LocateResponse, MapTileKey, locate callback registration, and cache-expiry callbacks for Python DataSourceServer.
• Adds Python bindings for Relation, Validity/MultiValidity, source-data references, TileSourceDataLayer, and source-data compound nodes.
• Forwards remote cache-expiry notifications through /cache-expired so Python datasources can receive Service cache refresh events.
• Adds a wheel smoke test covering feature/source-data/locate/cache-expired Python datasource APIs and updates the Python datasource example.

[sonarqubecloud]

Quality Gate passed

Issues
8 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Package	Line Rate	Branch Rate	Health
libs.geojsonsource.include.geojsonsource	100%	50%	✔
libs.geojsonsource.src	63%	36%	➖
libs.gridsource.include.gridsource	0%	0%	❌
libs.gridsource.src	0%	0%	❌
libs.http-datasource.src	47%	25%	❌
libs.http-service.include.mapget.http-service	100%	100%	✔
libs.http-service.src	55%	22%	➖
libs.logging.include.mapget	7%	3%	❌
libs.model.include.mapget.model	54%	30%	➖
libs.model.src	71%	40%	➖
libs.service.include.mapget.service	58%	50%	➖
libs.service.src	74%	37%	➖
Summary	62% (8325 / 13447)	32% (8706 / 27443)	➖

Minimum allowed line rate is 50%