Encode `LogMsg` using protobuf #15385

Job	Run time
paths-filter	5s
Checks / Rerun lints	37s
Checks / Check if running codegen would produce any changes	1m 23s
Checks / Lint markdown	23s
Checks / Spell Check	6s
Checks / Misc formatting	14s
Checks / markdown-paths-filter	4s
C++ tests	0s
Python Checks	0s
Deploy Landing Preview	0s
Minimum CLI Build / Set Config (linux-x64)	4s
Rust Checks / Test on ${{ matrix.name }}	0s
Rust Checks / Rust lints (fmt, check, clippy, tests, doc)	9m 30s
Build rerun_js / Build rerun_js	3m 33s
Build web viewer / Build web viewer	3m 10s
Checks / Check links	0s
Minimum CLI Build / Build rerun-cli (ubuntu-latest-16-cores)	5m 29s
Upload Web / Upload web build to google cloud (wasm32 + wasm-bindgen)	13s
Minimum Wheel Build / Set Config (linux-x64)	1s
Minimum Wheel Build / Build Wheels (ubuntu-latest-16-cores)	2m 29s
Minimum Wheel Test / Set Config (linux-x64)	4s
Minimum Wheel Test / Test Wheels (ubuntu-latest-16-cores)	3m 11s
	30m 36s

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