feat: remove pysam and bwa warmup hack

[clintval]

It is mentioned pysam.AlignmentFile internally buffers stdin so a hack was devised to "warm it up".

However, fgpyo.sam.reader and pysam.AlignmentFile are not needed and only provide code indirection since we can build the SAM header and all subsequent records using the from_text()/fromstring() methods of each.

[clintval]

Although we no longer need to override this method, it should have conformed to the same shape as the superclass:

def close(self) -> bool:
    self._reader.close()
    return super().close()

[clintval]

Because of: https://github.com/fulcrumgenomics/prymer/pull/65/files#r1787936312

[codecov]

Codecov Report

Attention: Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.

Project coverage is 97.25%. Comparing base (5515d05) to head (80ea938).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
prymer/offtarget/bwa.py	84.61%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
- Coverage   97.38%   97.25%   -0.13%     
==========================================
  Files          25       25              
  Lines        1605     1603       -2     
  Branches      302      303       +1     
==========================================
- Hits         1563     1559       -4     
  Misses         23       23              
- Partials       19       21       +2     

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[clintval]

I have one strangely failing test on GitHub CI (but not locally):

FAILED tests/offtarget/test_bwa.py::test_header_is_properly_constructed - AssertionError: assert {'PG', 'SQ'} == {'HD', 'PG', 'SQ'}
  Extra items in the right set:
  'HD'
  Full diff:
  - {'HD', 'PG', 'SQ'}
  ?  ------
  + {'PG', 'SQ'}

Will debug...

EDIT: the issue is we were using the old bwa repo in FG's org.