fix: cap mcp dependency below 2.0 and use instructions kwarg (adopted from #326)

[K4bain]

Adopted from #326 (original patch by @Daniyal0100101) — rebased onto current main and verified.

Why this is needed

pyproject.toml declares mcp>=1.12.0 with no upper bound. mcp 2.x is now out, and under 2.x this package fails at import/collection time (the lowlevel Server API was redesigned — the list_tools/call_tool decorator registration no longer exists). Every fresh pip install fastapi-mcp currently resolves to mcp 2.x and is broken out of the box.

This PR:

1. Caps the dependency at mcp>=1.12.0,<2.0.0 so installs resolve to a known-good mcp 1.x.
2. Passes the server description via the instructions= kwarg instead of the removed positional description argument (forward-compatible with mcp 1.x).

Verification

• Full unit suite: 69 passed against mcp 1.29.1 (latest 1.x).
• Without this cap, on mcp 2.1.1 the test suite fails during collection (ImportError from mcp.shared.memory).

Proper mcp 2.x support (adapting setup_server() to the new handler-registration API) is follow-up work; this PR stops the bleeding for new installs.

[Daniyal0100101]

I’ve closed #326 now that this PR supersedes it. The CI run here is also blocked on the same fork approval gate, and I only have read access to the repo. @itay-tadata, could you approve the workflow when you get a chance?