fix: bridge tool-calls in copilot-acp adapter

[teknium1]

Summary

Enables Hermes tool execution through the copilot-acp adapter. Previously, the adapter explicitly told the ACP backend "Do not emit OpenAI tool-call JSON" — the backend could only respond in prose, never actually calling tools.

Changes

• Pass tool schemas and tool_choice into the ACP prompt text so the backend knows what tools are available
• Instruct ACP backend to emit structured <tool_call>{...}</tool_call> blocks
• Parse XML tool-call blocks back into Hermes-compatible SimpleNamespace objects
• Bare JSON fallback regex for backends that emit raw JSON without XML tags
• Set finish_reason='tool_calls' when tool calls are extracted
• Clean tool-call markup from response text before passing to the agent

Follow-up fix

Fixed duplicate tool call extraction bug in original PR — when both XML block regex and bare JSON regex matched the same content, the same tool call was extracted twice. XML blocks now take precedence; bare JSON fallback only runs when no XML blocks are found.

What was stripped from original PR

• Heuristic fallback system (_heuristic_fallback_tool_calls) that auto-synthesized tool calls from prose — dangerous because it bypasses model judgment
• Portuguese-language patterns in regexes and intent detection — adapter should be language-agnostic
• Vision/terminal-specific hardcoded fallbacks

Validation

• 12 E2E tests covering: XML block parsing, bare JSON parsing, multiple calls, auto-generated IDs, invalid JSON handling, dict→string argument serialization, empty/None inputs, prompt formatting with/without tools, duplicate prevention, SimpleNamespace shape verification

Salvaged from PR #4536 by @MestreY0d4-Uninter — contributor authorship preserved in commit.