Refactor PQDSA_KEY set_raw functions to use goto-err cleanup

[dkostic]

Description of changes:

Consolidates error handling, fixes memory leaks on reuse, and
ensures atomic key assignment (no partial state on failure).

Call-outs:

Point out areas that need special attention or support during the review process. Discuss architecture or design changes.

Testing:

How is this change tested (unit tests, fuzz tests, etc.)? Are there any testing steps to be verified by the reviewer?

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.14286% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.32%. Comparing base (24d4627) to head (21103bb).

Files with missing lines	Patch %	Lines
crypto/fipsmodule/pqdsa/pqdsa.c	87.14%	9 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2993   +/-   ##
=======================================
  Coverage   78.31%   78.32%           
=======================================
  Files         689      689           
  Lines      120967   120970    +3     
  Branches    16963    16958    -5     
=======================================
+ Hits        94735    94745   +10     
+ Misses      25334    25329    -5     
+ Partials      898      896    -2     

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