Mitigate AssertionError for unique constraints

[hab6]

Description

Additional improvements that follow PR #52, which provided partial relief to address failing tests involving reflection of tables containing unique constraints. More work was needed in overloaded method IngresDialect::get_unique_constraints to return the correct constraint list in a proper format.

It is also worth noting that a few changes to requirements.py to be delivered in this PR should have been included in PR #52. Without those changes, the code delivered in PR #52 will still have problems.

Refactoring of get_unique_constraints

The logic of get_unique_constraints was refactored so that this method is now returns a list of dictionaries, with each dictionary containing the name and column(s) of a unique constraint.

It is worth noting that if the constraint name was auto-generated by the SQL engine (versus explicitly named in the application's CREATE TABLE statement), the constraint name is returned as None (following the example of the SQLite dialect).

Example of constraint data returned from IngresDialect::get_unique_constraints

[ {'name': None, 'column_names': ['data']},
  {'name': 'zz_dingalings_multiple', 'column_names': ['address_id', 'dingaling_id']},
  {'name': 'user_tmp_uq_main', 'column_names': ['name']} ]

Testing

1. Configure SQLAlchemy dialect compliance suite testing according to the instructions in README.testsuite.md
2. Run unique_constraints tests:
   pytest --db ingres_odbc -vv --maxfail=100 .\test\dialect\test_suite.py -k "test_get_multi_unique_constraints" --tb=no

Impact of Fix

Results when running test_get_multi_unique_constraints of the SQLAlchemy dialect compliance suite.

Results	Passed	Failed
Before Changes	26	16
After Changes	41	1

Environment

Microsoft Windows [Version 10.0.19045.4291]
Python 3.10.7
mock              5.1.0
packaging         24.0
pip               24.0
pluggy            1.5.0
pyodbc            5.1.0
pyproject-api     1.6.1
pypyodbc          1.3.6
pytest            8.2.1
setuptools        63.2.0
SQLAlchemy        2.0.29.dev0
sqlalchemy-ingres 0.0.7.dev5
tox               4.15.0
typing_extensions 4.12.0
virtualenv        20.26.2

Internal ticket II-14398