Cheroot incorrectly allows whitespace after HTTP versions

[kenballus]

❓ I'm submitting a ...

• 🐞 bug report
• 🐣 feature request
• ❓ question about the decisions made in the repository

🐞 Describe the bug. What is the current behavior?
RFC 9112 defines the following grammar rule for request lines:

request-line = method SP request-target SP HTTP-version

Cheroot accepts whitespace after the HTTP-version, even though this is not allowed by the grammar rule above.

❓ What is the motivation / use case for changing the behavior?
RFC compliance.

💡 To Reproduce

1. Start a Cheroot server.
2. Send it the following request:

GET / HTTP1.1 \r\n
Host: whatever\r\n
\r\n

3. Observe that the server responds 200.

💡 Expected behavior
The server should respond 400.

📋 Environment

• Cheroot version: 10.0.2.dev71+g1ff20b18
• Python version: 3.11.9
• OS: Linux 6.9.1