Fix plain COPY crash and restore copy_test to test suite

[SandeepDave2]

Issue-
Running a plain COPY with the ODBC loader was failing with ERROR 3399: InvokeSetupUDL(): UDx side process has exited abnormally. The external table path worked fine, only plain COPY crashed.

Root Cause-
I traced it back to commit eae4c95 (#19), which added column pruning. That change made the code use vidx.at(i) to map columns, and vidx only gets filled when the hidden column-filter params (query_col_name / query_col_idx) are sent.
On a plain COPY those params are sent but empty. Two things went wrong because of that:

1. The code still entered the column-filter block and built a broken query like SELECT FROM (...) (empty column list), which the remote DB rejected.
2. vidx stayed empty, so vidx.at(i) later threw an out-of-range and killed the process.

Fix-

• Only do column filtering when the column-name param is actually non-empty. If it's empty (plain COPY), build SELECT * FROM (...) and load all columns.
• If vidx is empty when we bind columns, default it to a straight 0..numcols-1 mapping, and set colInTable so the pre-null loop covers all columns. This keeps the plain COPY path behaving like it did before the change, so all columns line up correctly.

Testing-

• Tested a plain COPY against our source and it now loads all rows correctly (verified row count and data).
• Also restored copy_test in the Makefile test target.

[mkottakota1]

Apart from that changes are looking good

[mkottakota1]

I have reviewed the changes and analyzed the impact on adding " // Plain COPY: column-filter param present but empty -> load all columns.
query = "SELECT * FROM ( " + query + " ) sq" ;"

As requested in Teams, please run a sample program to load the specified columns.

[mkottakota1]

The changes are looking good and Fix is covering all the scenerios

[SandeepDave2]

I have reviewed the changes and analyzed the impact on adding " // Plain COPY: column-filter param present but empty -> load all columns. query = "SELECT * FROM ( " + query + " ) sq" ;"

As requested in Teams, please run a sample program to load the specified columns.

It's working as expected.