fix: Rebatch messages when restarting a publish stream

[dpcollins-google]

This prevents publishers which are network isolated for a while from appearing disconnected when the server attempts to acknowledge messages.

[codecov]

Codecov Report

Merging #496 (592118c) into master (980ce34) will increase coverage by 0.13%.
The diff coverage is 92.59%.

@@             Coverage Diff              @@
##             master     #496      +/-   ##
============================================
+ Coverage     75.38%   75.51%   +0.13%     
- Complexity      760      768       +8     
============================================
  Files           129      129              
  Lines          3875     3896      +21     
  Branches        174      179       +5     
============================================
+ Hits           2921     2942      +21     
+ Misses          850      849       -1     
- Partials        104      105       +1     

Impacted Files	Coverage Δ	Complexity Δ
...in/java/com/google/cloud/pubsublite/Constants.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
.../cloud/pubsublite/internal/wire/PublisherImpl.java	91.04% <92.59%> (+1.66%)	31.00 <6.00> (+7.00)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 980ce34...b3893f7. Read the comment docs.