Allow space separator in date-time regexes

[RFC 3339][0] is not very clear about what separator characters are
allowed. It just lists "space" as an example:

> NOTE: ISO 8601 defines date and time separated by "T".
> Applications using this syntax may choose, for the sake of
> readability, to specify a full-date and full-time separated by
> (say) a space character.

Ruby's [`DateTime.rfc3339`][1] allows `T`, `t`, and `\s`, so I'm going
with that. This should only affect the edge case tests since everything
else is delegated to `DateTime.rfc3339`.

There are a bunch of tests that were generated here: https://ijmacd.github.io/rfc3339-iso8601/
Thanks to @pboling for pointing me to it in: #153
The RFC 3339 examples include some that use an underscore as the
date-time separator, which I decided to ignore because it seems
arbitrary to allow random characters and Ruby doesn't support it.

[0]: https://datatracker.ietf.org/doc/html/rfc3339#section-5.6
[1]: https://github.com/ruby/ruby/blob/d3ea9070bbbf04749e5fcd8339d71a9e73a86cfb/ext/date/date_parse.c#L2613

Author: davishmcclurg

lib/json_schemer/format.rb

@@ -68,8 +68,9 @@ module Format
     end
 
     DATE_TIME_OFFSET_REGEX = /(Z|[\+\-]([01][0-9]|2[0-3]):[0-5][0-9])\z/i.freeze
-    HOUR_24_REGEX = /T24/.freeze
-    LEAP_SECOND_REGEX = /T\d{2}:\d{2}:6/.freeze
+    DATE_TIME_SEPARATOR_CHARACTER_CLASS = '[Tt\s]'
+    HOUR_24_REGEX = /#{DATE_TIME_SEPARATOR_CHARACTER_CLASS}24:/.freeze
+    LEAP_SECOND_REGEX = /#{DATE_TIME_SEPARATOR_CHARACTER_CLASS}\d{2}:\d{2}:6/.freeze
     IP_REGEX = /\A[\h:.]+\z/.freeze
     INVALID_QUERY_REGEX = /\s/.freeze
     IRI_ESCAPE_REGEX = /[^[:ascii:]]/