feat: Implement `GET /datasets/id` and `GET /datasets` (#3197)

* Rename model

* Add backend Dataset schema and `get` route for Datasets by ID

* Refactor app creation and test fixtures for API test harness

* Ruff 🐶

* Add timestamps to payload

* Use correct field names

* Ensure timestamps are serializable

* Flesh out test

* Use async client

* Add test for empty datasets

* Add another nontrivial example

* Ruff 🐶

* Resolve type annotation errors

* Update import

* Use default export path

* Create export directories in test env

* Try creating home directories?

* Do not mount UI route in test client

* Explicitly disable UI route on initialization

* Fix gnarly bug (properly skip prostgresql tests)

* Push example count into model

* Move serialization into route handler

* Use global ids for REST API

* Refactor server instrumentation

* Break up engine creation and instrumentation for clarity

* Remove engine from session factory wrapper

* Use updated httpx client syntax

* Improve type specificity for db dialect property

* Use explicit kwarg for sqlalchemy join

* Flesh out OpenAPI response schema for GET /datasets/id route

* Implement list datasets with cursor-based pagination

* Check dialect type when creating session factory

* Move API tests to `rest_v1` subdirectory for clarity

* Use hybrid property

* Properly try and return a value from hybrid property

* Use inplace expression