[Dev] Exception call chain

[ocots]

Feature: Exception Call Chain System for API Contextualization

Description

Following the successful migration of exceptions (100% completed), this project aims to implement a Call Chain System to contextualize exceptions at the API level.

Problem
Currently, exceptions provide detailed internal context (e.g., _validate_state_dimension) but fail to show the high-level user action, especially during nested API calls.

• Example: A user calls build_initial_guess, which calls initial_guess, which fails in initial_state. The current error only shows the initial_state context, hiding that the error originated from build_initial_guess and confusing the user about the source of the error.

Proposed Solution
Implement a thread-local tracking system to capture the hierarchy of public API calls and wrap exceptions with this full context.

Key Technical Components

1. Thread-Local Stack: A mechanism (push_api_call!, pop_api_call!) to track active API calls.
2. New Exception Types:
   • APICallInfo: Struct to store function name, signature, and user action description.
   • APICallChain: New exception type wrapping the original CTModelsException and the captured call_stack.
3. @api_function Macro: A macro to automate stack management and exception wrapping for public API functions.

Scope
Approximately 20-25 functions will be wrapped across 4 priority tiers:

• Tier 1 (Core): state!, control!, time!, dynamics!, objective!, build.
• Tier 2 (OCP Extended): variable!, constraint!, definition!, time_dependence!.
• Tier 3 (Initial Guess): initial_guess, build_initial_guess, validate_initial_guess.
• Tier 4 (Serialization): export_ocp_solution, import_ocp_solution.

Expected Outcome
Error messages will transparently display an "API Call Chain" section, detailing the path from the user's entry point down to the internal validation failure.