chore: adding camelcase flag keys to useFlags hook

[joker23]

depends on #1166

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Note

Medium Risk
Changes the shape and key access semantics of the deprecated useFlags() return value (including key filtering and event emission behavior), which can break consumers relying on raw flag keys or $ keys. Scope is limited to deprecated hook and related client/options plumbing, but it impacts runtime flag access and analytics events via variation() calls.

Overview
useFlags() (deprecated hook) now returns camelCased flag keys by default, with an opt-out via useCamelCaseFlagKeys exposed on the client as shouldUseCamelCaseFlagKeys() (defaulting to true in createClient and the server noop client). The proxy maps camelCase property reads back to the original flag key when calling client.variation(), and filters out $ system keys from the returned object.

The hook also avoids an extra mount-time render by skipping a redundant setFlags on first effect run, and updates tests/utilities accordingly (new toCamelCase helper + expanded useFlags test coverage for proxy semantics, caching, change events, context changes, and custom contexts).

^{Written by Cursor Bugbot for commit 697f71e. This will update automatically on new commits. Configure here.}

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[github-actions]

@launchdarkly/js-sdk-common size report
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Uncompressed size: 125383 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
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Uncompressed size: 84897 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 172375 bytes
Compressed size limit: 200000
Uncompressed size: 802016 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 22062 bytes
Compressed size limit: 24000
Uncompressed size: 114438 bytes

[joker23]

@cursor review

[devin-ai-integration]

✅ Devin Review: No Issues Found

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

View in Devin Review to see 4 additional findings.