Replace mutable maps with StateFlow for reactive Compose updates

[VictorB00]

Summary

• Replace ConcurrentHashMap in NubrickUser and FormRepository with MutableStateFlow, enabling Compose to reactively recompose when user properties or form values change via collectAsStateWithLifecycle
• Split HTTP request handling into compileHttpRequest (pure) and sendCompiledHttpRequest (IO) with new CompiledHttpRequest/CompiledHttpHeader data classes, allowing proper remember keying and avoiding redundant network calls
• Simplify rememberPageState and rememberNestedDataState by composing template variables directly instead of re-calling createVariableForTemplate
• Switch dependency from lifecycle-runtime-ktx to lifecycle-runtime-compose and move it to the nubrick module

Fixes https://github.com/plaidev/nativebrik/issues/2035

Test plan

• Verify pages load data correctly and display template variables
• Verify form inputs update template variables reactively
• Verify user property changes (e.g. setUserId, setProperty) reflect in the UI
• Verify nested data states render correctly
• Verify HTTP requests fire only when compiled request changes
• Run existing unit tests