mcp: add case senstive tests to the parser

[botengyao]

verify that a potential smuggling is not the problem.

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "backend__greet",
    "Name": "backend__secretTool",  // ← different casing
    "arguments": {"name": "Exploit"}
  }

#39174

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[agrawroh]

I was thinking if there are opportunities to parameterize the tests as they all seem to be validating the same thing. But maybe not as they are asserting on different sub-sections of the input JSON.