feature: AddTools logic should handle duplicated tool names

[edwardcqian]

Problem Statement

Currently one can override tools by accidentally adding two tools with the same name (e.g. typo in tool name causing two tools have the same name). It just silently overrides the duplicated tools.

Proposed Solution

There should at least be some warning or error message when attempting to add a tool which already exist in s.tools

Alternatives/Workarounds Considered

Alternative can just be to check for duplicate tool names while initializing the MCPServer.

[rwjblue-glean]

Definitely seems like something that we can make better. In order to add errors we'd have to do a bit of refactoring (plumb through err returns for AddTool and AddTools) , but that seems to be pretty straight forward.