fix: interaction between static args and HITL argument rewrite

[andreiancuta-uipath]

HITL guardrails can rewrite a tool call's arguments.
Previously, static args would be applied after HITL, which would overwrite the argument values back to the ones in the agent definition. In addition, the human would not see the static args in the HITL app interface.
This PR:

• Applies static args to the LLM tool calls, as early as possible. HITL sees the arguments after they have been processed by the static args layer, and the human's decision is final.
  • StaticArgsHandler is lazy; compared to the previous code, it computes tool schemas and static values only once, and caches the results.
  • This also simplifies the tool nodes and their wrappers.
• Fixes an edge case involving schema editing and $refs.
• Strips enum fields from IS tool schemas. This is to prevent validation errors when HITL alters a static argument, because the user-rewritten argument would not match the schema enum.