RobinTail / express-zod-api / 16398948654

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feat: `HEAD` method handling (#2816)

Based on #2791 

- MDN:
https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Methods/HEAD
- RFC: https://httpwg.org/specs/rfc9110.html#HEAD

> MUST NOT send content in the response

Findings in Express:

- no need to set `app.head()` handler, it's automatically set for all
`app.get()` ones:
  - https://expressjs.com/en/api.html#app.METHOD
- No extra handling required for `res.send()` — it automatically sends
`Content-Length` header instead of response body for requests having
`HEAD` method:
  - https://expressjs.com/en/api.html#res.send
- For streams, `Content-Length` should not be set anyway because of
`Transfer-encoding: chunked`, according to RFC:
  - https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.2
  - https://github.com/expressjs/express/issues/2893
- > A sender MUST NOT send a Content-Length header field in any message
that contains a Transfer-Encoding header field.
- HOWEVER, for `HEAD` it SHOULD be there: 
- The relevant nuance is described in [RFC 9110, Section 9.3.2.
HEAD(https://datatracker.ietf.org/doc/html/rfc9110#section-9.3.2):
- > The server SHOULD send the same header fields in response to a HEAD
request as it would have sent if the request had been a GET, except that
the payload header fields (Section 6.4) MAY be omitted. This includes
sending headers such as Content-Length, even though there is no response
body.
- And in [RFC 9110, Section 6.4.1.
Content-Length](https://datatracker.ietf.org/doc/html/rfc9110#section-6.4.1):
- > A server MAY send a Content-Length header field in a response to a
HEAD request (Section 9.3.2; see also Section 9.3.6), indicating the
size of the payload body that would have been sent had the request been
a GET.
- This means that even if a GET response would use chunked encoding and
omit Content-Length, the HEAD response can and should include
Content-Length if the size is known.

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