perf: optimize sending Channel messages in isolates

[blaugold]

Fixes #355

[codecov]

Codecov Report

Merging #389 (ea62fef) into main (2b96141) will increase coverage by 1.49%.
The diff coverage is 94.90%.

❗ Current head ea62fef differs from pull request most recent head 406ddbb. Consider uploading reports for the commit 406ddbb to get more accurate results

@@            Coverage Diff             @@
##             main     #389      +/-   ##
==========================================
+ Coverage   89.19%   90.69%   +1.49%     
==========================================
  Files         145      125      -20     
  Lines        9942     8918    -1024     
==========================================
- Hits         8868     8088     -780     
+ Misses       1074      830     -244     

Flag	Coverage Δ
e2e.cbl	90.69% <94.90%> (+0.02%)	⬆️
unit.cbl	?
unit.cbl_dart	?
unit.cbl_generator	?
unit.cbl_sentry	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...l/lib/src/service/serialization/serialization.dart	86.23% <86.66%> (-0.54%)	⬇️
packages/cbl/lib/src/service/cbl_service_api.dart	97.95% <94.33%> (-0.55%)	⬇️
...ackages/cbl/lib/src/database/proxy_blob_store.dart	100.00% <100.00%> (ø)
packages/cbl/lib/src/service/cbl_service.dart	98.75% <100.00%> (+<0.01%)	⬆️
packages/cbl/lib/src/service/channel.dart	86.70% <100.00%> (+0.81%)	⬆️
...rc/service/serialization/isolate_packet_codec.dart	100.00% <100.00%> (ø)
packages/cbl/lib/src/typed_data/annotations.dart	22.22% <0.00%> (-77.78%)	⬇️
packages/cbl/lib/src/support/edition.dart	50.00% <0.00%> (-50.00%)	⬇️
packages/cbl/lib/src/support/streams.dart	72.51% <0.00%> (-22.91%)	⬇️
packages/cbl/lib/src/support/isolate.dart	66.66% <0.00%> (-8.34%)	⬇️
... and 30 more

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