@W-21474595 - add MCP tool-level response token usage (responseCharCount)

[smuduganti-sf]

• Added calculateResponseCharCount() to compute total character count from tool result content.
• On each tool call, the response character count is computed and sent in the TOOL_CALLED telemetry event as responseCharCount.

What does this PR do?

@W-21474595@

What issues does this PR fix or reference?

[cristiand391]

This method only considers plain text from tool responses but tools can also have structured output, see:

https://modelcontextprotocol.io/specification/2025-11-25/server/tools#output-schema

mcp/packages/mcp-provider-code-analyzer/src/tools/run_code_analyzer.ts

Line 111 in b7efb41

structuredContent: output

I think the safe way would be to account for both since a tool seems to be able to return plain text + structured output

[iowillhoit]

I think i would feel better if this entire call was wrapped in a try/catch.

I never want this to cause a tool call to fail. Example:

let responseCharCount = 0;
try {
  responseCharCount = this.calculateResponseCharCount(result);
} catch {
  // never let telemetry instrumentation fail a tool call
}