Fix: unprivileged copy from

[aykut-bozkurt]

We did not cover the case where unprivileged user runs COPY FROM in our tests. COPY TO works well since we always convert relation to select statement, for which PG performs correct privilege checks during the copy. For COPY FROM, we need to perform these checks explicitly as done in DoCopy() at Postgres.

[codecov]

Codecov Report

Attention: Patch coverage is 92.77108% with 6 lines in your changes missing coverage. Please review.

Project coverage is 91.31%. Comparing base (29769de) to head (9d6b3fb).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/parquet_copy_hook/pg_compat.rs	90.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #125      +/-   ##
==========================================
- Coverage   91.34%   91.31%   -0.04%     
==========================================
  Files          91       91              
  Lines       13059    13140      +81     
==========================================
+ Hits        11929    11999      +70     
- Misses       1130     1141      +11     

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[marcoslot]

Probably some more tests with things like CREATE POLICY would be good

[aykut-bozkurt]

Probably some more tests with things like CREATE POLICY would be good

we already had pls tests for both copy from and copy to