[Server] HTTP Transport Header Compliance

[chr-hertel]

With the compliance report on HTTP method support / header handling @SamMorrowDrums discovered the PHP SDK responses come with 500.

See https://gist.github.com/SamMorrowDrums/9fb1191012cfcbb313e189af5a7c1fd9

Goal is to respond with 405 + Allow header.

[chr-hertel]

Hi @SamMorrowDrums, was just looking at this again, also while reviewing @dotmarn's solution.

How did you run into the 500s? Can't reproduce that right now
I just used the very first example:

php -S localhost:8000 examples/server/cached-discovery/server.php

And this is what I get with v0.3.0 and main:

And with #227:

[SamMorrowDrums]

@chr-hertel hey, thanks so much for looking into it, perhaps I made some mistakes in https://github.com/SamMorrowDrums/mcp-php-starter and the 500s could be my fault, apologies if that was a false alarm.