[ADDED] Atomic batch publish support

[AdamPayzant]

Adding 2.12 implementation for JetStream Batch Publishing (ADR-50)

[codecov]

Codecov Report

❌ Patch coverage is 58.82353% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.30%. Comparing base (6f0f5c4) to head (d313fe5).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/js.c	58.33%	10 Missing and 10 partials ⚠️
src/jsm.c	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #977      +/-   ##
==========================================
- Coverage   70.33%   70.30%   -0.03%     
==========================================
  Files          48       48              
  Lines       17447    17497      +50     
  Branches     3573     3582       +9     
==========================================
+ Hits        12271    12301      +30     
- Misses       1737     1748      +11     
- Partials     3439     3448       +9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.