android/ios: move static fields into Rust layer

[snowp]

Before this change a number of fields would be passed through to the Rust layer on every log call, resulting in extra JNI calls and string allocations. This PR moves a number of these fields into Rust allowing us to store them as reusable strings.

This also has the benefit that we can read these directly during crash reporting and not pass these through from the platform layer

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• CHANGELOG.md's "Unreleased" section has been updated, if applicable.

[github-actions]

Size Comparison Report (x86_64)

Metric	APK (KB)	SO (KB)
Baseline	3374	1252
Current	3374	1252
Difference	0	0

APK size unchanged. SO size unchanged.

[github-actions]

Android Benchmark Results

Device: PR: Emulator - Android SDK built for x86_64 (API 31) | main: Emulator - Android SDK built for x86_64 (API 31)

Note: Benchmarks run on emulator. Results may vary between runs and may differ from physical devices.

Allocations

Test	PR	main	Δ
logHttpNetworkLog50FieldsAndHeadersAndFieldProviders	1088	1043	+4.3%
logNotMatched10Fields	20	19	+5.3%
logNotMatched5000Fields	143	160	-10.6%
logNotMatched500Fields	143	132	+8.3%
logNotMatched5Fields	15	15	0.0%
logNotMatchedNoFields	1	1	0.0%
trackSpansWithFields	329	316	+4.1%
trackSpansWithoutFields	57	56	+1.8%

Timing

Test	PR	main	Δ
logHttpNetworkLog50FieldsAndHeadersAndFieldProviders	242.55 us	237.80 us	+2.0%
logNotMatched10Fields	6.65 us	6.63 us	+0.3%
logNotMatched5000Fields	2.71 ms	2.71 ms	0.0%
logNotMatched500Fields	277.70 us	277.69 us	+0.0%
logNotMatched5Fields	3.68 us	3.75 us	-1.8%
logNotMatchedNoFields	509 ns	545 ns	-6.6%
trackSpansWithFields	564.98 us	563.59 us	+0.2%
trackSpansWithoutFields	8.36 us	8.32 us	+0.5%