azure-cosmos needs typing updates for mypy version 2.1.0

**ACTION NEEDED:** This version of mypy will be merged on **2026-10-12**. The build will begin to fail for this library if errors are not fixed.

**Library name:** azure-cosmos
**Mypy version:** 2.1.0
**Mypy Build:** [Link to build (2026-07-26)](https://dev.azure.com/azure-sdk/internal/_build/results?buildId=6617598&view=logs&j=87f850b5-cf15-53c6-370a-4be21ee70ec7&t=c4b2a078-69a7-55a2-d776-67715c71590f)
**How to fix:** Run the `next-mypy` azpysdk command at the library package-level and resolve the typing errors.
1) `/mnt/vss/_work/1/s>pip install -e ./eng/tools/azure-sdk-tools`
2) `../azure-cosmos>azpysdk next-mypy --isolate .`

See the [Typing Guide](https://github.com/Azure/azure-sdk-for-python/blob/main/doc/dev/static_type_checking.md#run-mypy) for more information.

Start in the azure-cosmos package by installing eng/tools/azure-sdk-tools and running azpysdk next-mypy --isolate . at package level. Review the resulting typing errors and the linked static type-checking guide. Done means the reported errors are resolved and the library passes the mypy 2.1.0 check before the 2026-10-12 merge.

Written by the indexing model from the issue text.