fix: reject MAC address octets with a sign or whitespace (#424)

MacAddress.validate_mac_address parsed each octet with int(part, 16),
which also accepts a leading +/- sign and surrounding whitespace. As a
result strings like -a:-b:-c:-d:-e:-f, +a:+b:+c:+d:+e:+f and
" a: b: c: d: e: f" were accepted, with the sign/whitespace variants
silently normalized into a valid-looking MAC the caller never supplied.

Require both characters of each octet to be hex digits before the int()
conversion so malformed octets raise the mac_address_format error like
other invalid input.

HISTORY.md

@@ -2,6 +2,8 @@
 
 ## Latest Changes
 
+* fix(mac_address): reject MAC octets with a sign or whitespace (e.g. `-a:...`, `+a:...`, ` a:...`) that `int(..., 16)` accepted.
+
 ## 2.11.2
 
 * fix: accept common timezone abbreviations like EDT in TimeZoneName validator by @r266-tech in https://github.com/pydantic/pydantic-extra-types/pull/376