Django-clickhouse-backend

- Fix test db name when NAME not provided in DATABASES setting.
- Fix Enum error when provided an IntegerChoices value.
- Add document about multiple db settings.

- Add `return_int` parameter to `Enum[8|16]Field` to control whether to get an int or str value when querying from the database.
- Fix TupleField container_class.
- Add fields documentation.

- Add tests for migrations.
- Fix bytes escaping.
- Fix date and datetime lookup.
- Add documentations.
- Add lots of new field types:
- Float32/64
- [U]Int8/16/32/64/128/256
- Date/Date32/DateTime('timezone')/DateTime64('timezone')
- String/FixedString(N)
- Enum8/16
- Array(T)
- Bool
- UUID
- Decimal
- IPv4/IPv6
- LowCardinality(T)
- Tuple(T1, T2, ...)
- Map(key, value)

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- Add tests for backends.
- Remove redundant code.
- Correct database features.
- Fix bugs that find by new tests.

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- Adopt some testcase from django project.
- Fix bugs such as datetime escaping and update field use F expression.

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- ID worker interface changes and configuration item adjustments.
- Support database connection pool.
- Refactored the implementation of Engine to be more concise and stable.
- Database related features are concentrated in the SQLCompiler implementation.
- Ignore unsupported field-level db_index attribute, and AlterUniqueTogether migration operation in favor of django built-in model or 3rd party model migration.