Let SortAndBatchElements batches reach max_batch_weight

[anishmehta24]

SortAndBatchElements cut a batch when adding the next element would make it weigh exactly max_batch_weight, so batches never reached the limit. Four size-5 elements with max_batch_weight=10 came out as four batches of one instead of two batches of two.

Both DoFns now use > for the weight check, same as BatchElements. Added a test for each DoFn that fails on master; util_test.py passes.

fixes #40461

Written with help from Claude.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.56%. Comparing base (69bdf5f) to head (b16d34b).
⚠️ Report is 44 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #40462       +/-   ##
=============================================
+ Coverage     59.04%   79.56%   +20.51%     
=============================================
  Files          2797      487     -2310     
  Lines        280750    82225   -198525     
  Branches      12488        0    -12488     
=============================================
- Hits         165764    65420   -100344     
+ Misses       108540    16805    -91735     
+ Partials       6446        0     -6446     

Flag	Coverage Δ
go	?
java	?
python	79.56% <ø> (-0.11%)	⬇️

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[github-actions]

Assigning reviewers:

R: @shunping for label python.

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[shunping]

LGTM! Thanks for fixing this.