Enable cross-platform HttpClient usage

[devnatan]

We need to restructure our codebase to enable native implementation of HttpClient configuration and related code.

1. Move Resource API classes to common sourceSet

   • Migrate all *Resource API classes from platform-specific sourceSets to the common sourceSet
   • Remove existing expect/actual declarations from these classes since they'll now be shared across all platforms
   • Identify Resource API implementations that aren't yet supported in Kotlin/Native.

2. Add expect/actual for Native-incompatible implementations

   • Identify HttpClient configuration implementations that aren't yet supported in Kotlin/Native (e.g. UnixSocketFactory due to OkHttp - only supports JVM)
   • Create expect declarations in common for these unsupported implementations
   • Provide actual implementations for JVM platform
   • Add appropriate Native stubs or alternative implementations as needed