http: make the RTSP version check stricter

- make it only accept version 1.0, as that is the version curl supports
- convert the parser to use strparse
- the status code max is now 999, but it does allow != 3 digits

Closes #16435

docs/internals/STRPARSE.md

@@ -151,6 +151,15 @@ int Curl_str_casecompare(struct Curl_str *str, const char *check);
 Returns true if the provided string in the `str` argument matches the `check`
 string case insensitively.
 
+## `Curl_str_cmp`
+
+~~~c
+int Curl_str_cmp(struct Curl_str *str, const char *check);
+~~~
+
+Returns true if the provided string in the `str` argument matches the `check`
+string case sensitively. This is *not* the same return code as `strcmp`.
+
 ## `Curl_str_nudge`
 
 ~~~c