chore: adding custom event when evaluating from RSC

[joker23]

WIP - but pushing this up early to get some discussions

This PR will make it so that every React Server session will batch in a custom event (event payload TBD) so we can have a way to track usage

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Note

Medium Risk
Adds a new track requirement to LDServerBaseClient and triggers an extra analytics event on the first server-side variation call, which could impact integrations that provide custom clients and may introduce unexpected event volume.

Overview
React server sessions now emit a single custom track event ($ld:react-sdk:rsc-evaluation) the first time any *Variation/*VariationDetail method is called via createLDServerWrapper, to measure React Server Component evaluation usage.

LDServerBaseClient is extended to require track(...), tests are refactored to share a makeMockServerClient (now including track), and a new rscTracking test suite asserts the one-time tracking behavior; example formatting tweaks to CSS/tsconfig.json are also included.

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[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 25661 bytes
Compressed size limit: 26000
Uncompressed size: 126143 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 23240 bytes
Compressed size limit: 24000
Uncompressed size: 121325 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 172915 bytes
Compressed size limit: 200000
Uncompressed size: 804043 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 24994 bytes
Compressed size limit: 25000
Uncompressed size: 86916 bytes

[joker23]

@cursor review

[cursor]

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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[joker23]

Real review for this starts here. Previous files are lint and test changes