✨ API client class

[JWCook]

Current docs here (preview): https://pyinaturalist.readthedocs.io/en/main/user_guide/client.html

This issue is for tracking overall progress on iNatClient (originally discussed in #163). This will be a higher-level interface that will be easier to configure, maintain some basic state information, and return model objects instead of JSON.

Once these issues and the issues listed #230 are complete, pyinaturalist will be ready for a 1.0 release.

General features

• Add models for API response objects #145
• Add basic structure for API client class #163
• Automatically document controller methods based on lower-level request functions #220
• Add configurable retry + backoff settings #209
• Refactor existing request functions to accept all settings used by iNatClient #219
• Add support for iNatClient default params to pass to all requests #237
• Add integration with requests-cache #158
• Add auto-refreshing access tokens to iNatClient #233
• Cache access tokens until they expire #236
• Add async-compatible Paginator for iNatClient results #276
• Batch requests by ID that exceed the max URL length for GET requests #248
• Complete test coverage for iNatClient + controllers #234
• Complete documentation for iNatClient, controller methods, and models #432

Controllers

• Implement Observation controller: read-only methods #218
• Implement Observation controller: create/update/delete/upload #221
• Implement Taxon controller #222
• Implement Place controller #223
• Implement Project controller #224
• Implement Identifications controller #259
• Implement ControlledTerms controller #260
• Implement Users controller #261
• Implement Posts controller #262
• Implement ObservationField controller #265