Remove fixed suffix /sse

[adamglin0]

Remove the hardcoded /sse string in the sse client transport, which forcibly adds /sse to the path, making it very crude.

When using all sse mcp servers, it's almost always in the format like http://localhost:3000/sse, and the forced addition of /sse leads to errors. In (npx @modelcontextprotocol/inspector), users also need to manually add the /sse suffix.

Motivation and Context

How Has This Been Tested?

Breaking Changes

If this PR is merged, consumers must manually add the /sse suffix to their URL.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[StefMa]

This is an breaking change!
Consumers might relay on /sse suffix.
They can easily fix it, but they have to be aware of it.

[Mervap]

This is indeed a breaking change, but the current assumption simply doesn’t work for some MCP implementations.
A major version bump would clearly indicate that the release may include breaking changes

Please approve this PR, as it’s currently nearly impossible to use the client with servers that don’t end with /sse