refactor: react contract tests

[joker23]

No description provided.

[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: 29000
Uncompressed size: 126143 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 31334 bytes
Compressed size limit: 34000
Uncompressed size: 111335 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 179090 bytes
Compressed size limit: 200000
Uncompressed size: 828524 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 36750 bytes
Compressed size limit: 38000
Uncompressed size: 201859 bytes

[joker23]

This should not be shared as different clients might need to specify different capabilities. But we can make a capability type that is relevant to both server and client. The capabilities are listed in https://github.com/launchdarkly/sdk-test-harness/blob/v2/docs/service_spec.md