add batching for mtz files

[kmdalton]

This attempts to address #344 to enable batching with dataset.write_mtz. I could use some eyes on this control flow.

This changes the signature for rs.DataSet.write_mtz adding batch=True and batch_key=None options. write_mtz will generate a naive set of batches in the header if batch is truthy. batch_key will be inferred and is only explicitly needed of there are multiple columns with BATCH dtype. batch=False and batch_key is not None will raise a ValueError.

[codecov]

Codecov Report

❌ Patch coverage is 84.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.84%. Comparing base (d65b8ee) to head (91b921d).

Files with missing lines	Patch %	Lines
reciprocalspaceship/io/mtz.py	84.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #345      +/-   ##
==========================================
- Coverage   86.86%   86.84%   -0.03%     
==========================================
  Files          40       40              
  Lines        2856     2881      +25     
==========================================
+ Hits         2481     2502      +21     
- Misses        375      379       +4     

Flag	Coverage Δ
unittests	86.84% <84.00%> (-0.03%)	⬇️

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[JBGreisman]

Overall, this looks good to me. I still want to test it out a bit more before fully approving the change. Just wanted to confirm two things first:

1. Are these read properly by aimless?
2. Are these read by phenix in methods such as the table 1 generator, etc that take unmerged data?

[kmdalton]

Overall, this looks good to me. I still want to test it out a bit more before fully approving the change. Just wanted to confirm two things first:

1. Are these read properly by aimless?

2. Are these read by phenix in methods such as the table 1 generator, etc that take unmerged data?

Valid concerns. I agree we should confirm before merging.

[JBGreisman]

looks fine to me -- I think we should just confirm it behaves with phenix / aimless before merging.