feat: Support ldcli's dev-server

[ynishinaka]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

Describe the solution you've provided

The LaunchDarkly CLI provides a development server for local testing (https://docs.launchdarkly.com/guides/flags/ldcli-dev-server). Its streaming format is slightly different than stream.launchdarkly.com in that:

• it lacks segments field;
• it emits an additional newline after comment (:\n\n as opposed to :\n).

To overcome these differences, I modified how it parses JSON and server-sent events. I've confirmed that stack test passed for lts-20.26.

Describe alternatives you've considered

Additional context

BEGIN_COMMIT_OVERRIDE
fix: Fix SSE newline handling
fix: Handle optional properties in data payload
END_COMMIT_OVERRIDE

[keelerm84]

@ynishinaka thank you so much for your contribution!

I have released those changes under v4.4.1. Thanks!