Cleanup of deprecated code and features

[Mr3zee]

Strict mode Migration
A series of changes to simplify kRPC protocol

• Remove fields support
• Remove stream scopes
• Simplify lifetime management
• Cold RPC clients creation
• Deprecated declarations cleanup
• Documentation update for previous changes

Subsystem
All, mostly kRPC

Problem Description
A lot of deprecated code is left out after the previous changes

Solution
Cleanup!

[Copilot]

Pull Request Overview

This PR cleans up deprecated code and features for the kRPC protocol. It removes unused APIs and strict mode functionality, refactors strict mode diagnostics into new objects, and removes deprecated CLI options and redundant functions.

• Removed deprecated functions and classes in the core API.
• Refactored strict mode diagnostics and checkers in the compiler plugin.
• Removed deprecated CLI options and API endpoints no longer in use.

Reviewed Changes

Copilot reviewed 60 out of 60 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
core/api/core.api	Removed deprecated utility classes and functions no longer used in kRPC.
compiler-plugin/compiler-plugin-k2/src/main/v_2_2_2/kotlinx/rpc/codegen/checkers/FirRpcCheckersVS.kt	Removed outdated strict mode expression checker for stream scopes.
compiler-plugin/compiler-plugin-k2/.../diagnostics/DiagnosticFactories.kt (various)	Removed legacy diagnostic factories and related strict mode support.
compiler-plugin/compiler-plugin-k2/src/main/latest/kotlinx/rpc/codegen/checkers/FirRpcCheckersVS.kt	Simplified strict mode class checker by removing the unnecessary context parameter.
compiler-plugin/compiler-plugin-core/.../RpcDiagnosticRendererFactory.kt	Refactored strict mode diagnostic mapping into an object using the new API.
compiler-plugin/compiler-plugin-k2/src/main/core/kotlinx/rpc/codegen/StrictMode.kt	Removed the strict mode configuration file and related code.
compiler-plugin/compiler-plugin-backend/.../RpcStubGenerator.kt	Removed the deprecated getFields function from stub generation.
compiler-plugin/compiler-plugin-backend/.../RpcIrContext.kt	Removed unused IR symbols no longer required after deprecation

Comments suppressed due to low confidence (3)

compiler-plugin/compiler-plugin-cli/src/main/latest/kotlinx/rpc/codegen/RpcCompilerPlugin.kt:18

• Deprecated strict mode CLI options have been removed from pluginOptions. Please update the accompanying documentation to guide users on the new configuration approach.

StrictModeCliOptions.STATE_FLOW, StrictModeCliOptions.SHARED_FLOW, StrictModeCliOptions.NESTED_FLOW, StrictModeCliOptions.STREAM_SCOPED_FUNCTIONS, StrictModeCliOptions.SUSPENDING_SERVER_STREAMING, StrictModeCliOptions.NOT_TOP_LEVEL_SERVER_FLOW, StrictModeCliOptions.FIELDS,

compiler-plugin/compiler-plugin-backend/src/main/core/kotlinx/rpc/codegen/extension/RpcStubGenerator.kt:617

• The generateGetFieldsFunction call has been removed. Ensure that all consumers relying on this API are updated to use the new mechanism or removed accordingly.

generateGetFieldsFunction()

compiler-plugin/compiler-plugin-k2/src/main/core/kotlinx/rpc/codegen/StrictMode.kt:1

• The removal of StrictMode.kt requires verifying that all configuration processes and strict mode handling in the compiler plugin have been updated to use the new diagnostics system.

Entire file removed