Tests can signal immediate rebroadcast

[gammazero]

No more need to update a synchronizd timer.

[codecov]

Codecov Report

Attention: Patch coverage is 88.57143% with 4 lines in your changes missing coverage. Please review.

Project coverage is 60.34%. Comparing base (e2d2f36) to head (baf4e71).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...tswap/client/internal/messagequeue/messagequeue.go	88.57%	4 Missing ⚠️

@@            Coverage Diff             @@
##             main     #726      +/-   ##
==========================================
- Coverage   60.37%   60.34%   -0.04%     
==========================================
  Files         244      244              
  Lines       31044    31029      -15     
==========================================
- Hits        18743    18724      -19     
- Misses      10632    10634       +2     
- Partials     1669     1671       +2     

Files with missing lines	Coverage Δ
...tswap/client/internal/messagequeue/messagequeue.go	84.98% <88.57%> (-0.44%)	⬇️

... and 10 files with indirect coverage changes