fix(plugins): export real tool args when payload.args is a CopyOnWriteDict

[Sanjays2402]

Closes #5699

📌 Summary

ToolsTelemetryExporter always exported tool.invocation.args as {} on the tool.pre_invoke span, even when the tool was invoked with real arguments, so tool telemetry lost all input data.

🔁 Reproduction Steps

Issue #5699. Offline reproduction of the root cause:

>>> import orjson
>>> from cpex.framework.memory import CopyOnWriteDict
>>> orjson.dumps(CopyOnWriteDict({"sysid": "PRD", "client": "999"}), default=str)
b'{}'
>>> orjson.dumps(dict(CopyOnWriteDict({"sysid": "PRD", "client": "999"})), default=str)
b'{"sysid":"PRD","client":"999"}'

🐞 Root Cause

tool_pre_invoke passes payload.args straight to orjson.dumps (plugins/tools_telemetry_exporter/telemetry_exporter.py:171). When the plugin framework hands over a cpex.framework.memory.CopyOnWriteDict, orjson serializes a dict subclass by reading its internal C-level storage and bypasses the Python-level overrides the copy-on-write wrapper relies on. The backing shell is empty, so the export is {} while repr() and normal access show the real arguments.

💡 Fix Description

Convert to a plain dict before dumping. One line, no behaviour change for the plain-dict case (nested values are already plain containers).

📏 Reviewability

• This PR has one clear purpose
• The linked issue is not labeled triage
• Unrelated bugs or improvements are tracked in separate issues/PRs
• Tests are included with the code they validate
• If AI-assisted, I understand and can explain the generated changes

🧪 Verification

New test_pre_invoke_exports_copy_on_write_args in the plugin's existing test module. Verified fail-without-fix / pass-with-fix by stashing the source change:

Check	Command	Status
Plugin unit tests	pytest tests/unit/mcpgateway/plugins/plugins/tools_telemetry_exporter/	6 passed
New test without the source fix	same, -k copy_on_write	1 failed (expected)
Lint / format	ruff check, ruff format --check on both changed files	clean

📐 MCP Compliance (if relevant)

• Matches current MCP spec
• No breaking change to MCP clients

✅ Checklist

• Code formatted (make black isort pre-commit)
• No secrets/credentials committed