feat: add Template.write_to()

[msto]

Addresses #60

[codecov-commenter]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (d2d50c4) 92.36% compared to head (c5baf25) 92.85%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #62      +/-   ##
==========================================
+ Coverage   92.36%   92.85%   +0.49%     
==========================================
  Files          30       30              
  Lines        2972     2996      +24     
  Branches      544      552       +8     
==========================================
+ Hits         2745     2782      +37     
+ Misses        160      143      -17     
- Partials       67       71       +4     

Files	Coverage Δ
fgpyo/sam/__init__.py	87.28% <100.00%> (+4.04%)	⬆️
fgpyo/sam/tests/test_template_iterator.py	100.00% <100.00%> (ø)

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