Added method get_unique_constraints II-14372

[hab6]

Description

Added reflection method get_unique_constraints to retrieve names of existing unique constraints.

Error fixed when running the SQLAlchemy dialect compliance suite

File "C:\.....\sqlalchemy\lib\sqlalchemy\engine\interfaces.py", line 1613,
 in get_unique_constraints
raise NotImplementedError()
NotImplementedError

Testing - How to reproduce (before fix)

1. Configure SQLAlchemy dialect compliance suite testing according to the instructions in README.testsuite.md
2. Run unique_constraints tests:
   pytest --db ingres_odbc --maxfail=100 test_suite_reflection.py -k "test_get_multi_unique_constraints"

Impact of fix

Results	Passed	Failed
Before Fix	0	42
After Fix	26	16

The remaining 16 failed tests are caused by different issues and will be handled separately.

Environment

Microsoft Windows [Version 10.0.19045.4291]
II 11.2.0 (a64.win/100) 15807
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            8.2.0
setuptools        63.2.0
SQLAlchemy        2.0.29.dev0
sqlalchemy-ingres 0.0.7.dev4ingres
tox               4.15.0
typing_extensions 4.11.0
virtualenv        20.26.2

Internal ticket II-14372

[clach04]

Nothing but good things to save about this. I suspect we need at least a few additional tests added to (our) test suite.

It's been a while since I got my hands dirty with Ingres specific schemas. I think this change will work fine for ANY DDL issued via SA (orm). I suspect it will miss a few cases:

1. modify table to BTREE/ISAM unique - I do NOT think this shows up in that meta data table
2. create index unique - same as above

Constraints are created under the covers as case number 2 above BUT show up in additional syscats.

Recommend manual test for now, if I'm wrong we're done. If I'm correct then open new issue and get this merged with a link.

[hab6]

Opened new issues prompted by comments

#53 Create test suite for the SQLAlchemy Ingres connector
#54 Add support for unique constraints when using BTREE & ISAM
#55 Review Ingres dialect support for unique indexes