Top-level map columns reflect as String

[aminghadersohi]

Problem

AthenaDialect._get_column_type now reflects array<...> and nested map/struct types, but a top-level map<string,int> column still reflects as String, so the key and value types are lost for inspectors and autoload_with tables.

Reproduction

from pyathena.sqlalchemy.base import AthenaDialect
AthenaDialect()._get_column_type('map<string,int>')   # String()
AthenaDialect()._get_column_type('array<map<string,int>>').item_type  # AthenaMap(...)

Environment

PyAthena 3.35.4 and master (c01c56f), Python 3.11, SQLAlchemy 2.0.52, Athena engine version 3.

Proposed fix (optional)

Apply the nested map branch at the top level too, returning AthenaMap(key_type, value_type).

[laughingman7743]

Confirmed. _get_column_type only takes the map and row/struct branches when _nested is set; #755 / PR #774 deliberately limited typed reflection to ARRAY columns, so top-level map<...> still reflects as String. The same applies to top-level struct<...> / row(...) columns, which this issue does not mention. Please widen the scope to cover both so reflection is consistent, returning AthenaMap(...) and AthenaStruct(...) respectively.

This changes the reflected type of existing columns from String, so it will be release-noted as a behavior change.

Per CONTRIBUTING.md, please validate against a real table (Glue metadata and the information_schema fallback both feed this code) in your own AWS environment and record before/after results in the PR's TEST section. External-fork PRs are not run in the project's AWS CI.

[laughingman7743]

Target master for the fix; the maintainers will port it to the 3.x maintenance branch afterwards, so please do not open a PR against 3.x.

[laughingman7743]

If you plan to send a PR for this, please say so here. If the issue stays open for a long time without a PR, the maintainers may pick it up and implement the fix themselves.