MCP-CustomTool: Handle duplicate tool names, if any

[souvikghosh04]

MCP tool names should be unique. Custom tools when configured and exposed should not be duplicate and conflict with existing tool names.

• MCP tools should not be duplicate
• Tools of both types- BuiltInTool and DynamicCustomTool should be unique
• This should be detected and validated during tools registration
• Appropriate error message should be provided to user if that happens so that user can fix it
• Add supporting tests with good code coverage and different scenarios and edge cases

[JerryNixon]

Remember tool names are based on Entity aliases which are already required to be unique.