fix(sql): preserve source qualifiers in CTAS with explicit schema

[lyne7-sc]

Which issue does this PR close?

• Closes CTAS with an explicit schema fails for qualified columns with the same name #23878.

Rationale for this change

CTAS with an explicit schema fails when qualified source columns have the same name because their qualifiers are not preserved.

What changes are included in this PR?

• Preserve source column qualifiers in the CTAS cast projection.
• Add a SQL logic test for this case.

Are these changes tested?

Yes.

Are there any user-facing changes?

This is a bug fix with no public API changes.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.65%. Comparing base (1c8295c) to head (fae3a8b).
⚠️ Report is 41 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23879      +/-   ##
==========================================
- Coverage   80.75%   80.65%   -0.11%     
==========================================
  Files        1089     1091       +2     
  Lines      368809   371031    +2222     
  Branches   368809   371031    +2222     
==========================================
+ Hits       297837   299244    +1407     
- Misses      53217    53940     +723     
- Partials    17755    17847      +92     

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