Fix iterable selections for entity and collection requests

[Shubham-Padkonde]

Fixes #71.

Normalize iterable selections into a comma-separated string before building the query. Both EntityGetRequest.select() and QueryRequest.select() use the same helper, so .select(['NameFirst', 'NameLast']) produces one $select value rather than serializing the Python collection. Iterators are consumed once when setting the selection.

Existing string inputs, fluent chaining, and .select(None) retain their behavior. The method documentation and changelog describe the supported input.

Validation: all 306 tests pass, including networking integration tests. Six iterable regressions fail before the fix; two additional cases cover strings and clearing the selection. Pylint passes at 10/10, and the pinned Flake8 passes under Python 3.10 (its entry-point discovery is incompatible with Python 3.12).

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[phanak-sap]

Hii @Shubham-Padkonde, thanks for the PR.

• please sign the CLA it cannot be merged without it.
• since you jumped on quite old issue, it would perhaps make sense to cover the related the method select of ODataQuery classes should handle $select=* #73
• seems to me that this comment in the method select of ODataQuery classes should handle iterable parameters #71 was missed: the method select of ODataQuery classes should handle iterable parameters #71 (comment)