Fix Regex(flags=re.I) crashing on CPython <= 3.10 and PyPy (#246)

[vineethsaivs]

What

Constructing a Regex with an actual re flag crashes on CPython <= 3.10 and PyPy:

import re
from schema import Regex
Regex(r"foo", flags=re.IGNORECASE)
# ValueError: Unknown format code 'b' for object of type 'str'

re.IGNORECASE and the other re.* flags are re.RegexFlag (an IntFlag) members, not plain ints. Regex.__init__ builds the human-readable flag list with

Regex.NAMES[i] for i, f in enumerate(f"{flags:09b}") if f != "0"

On CPython <= 3.10 and PyPy, applying the b format code to an IntFlag routes through Enum.__format__, which formats the member via its string form ("re.IGNORECASE") and then rejects the b code, raising ValueError. This happens before re.compile(...), so Regex(pattern, flags=<any re flag>), the natural documented usage, is completely unusable on those versions; passing a plain int works, which is why it slipped past the tests.

Fix

Coerce to int before the binary formatting (f"{int(flags):09b}"). re.compile already accepts the enum unchanged, so only the repr computation needed the coercion. The rendered output is byte-identical for the existing int-flag usage.

Test

Added test_regex_flags: it constructs Regex with re.IGNORECASE and with re.IGNORECASE | re.MULTILINE, and asserts both validate correctly and the flag name appears in the repr. It fails before the change (ValueError) on affected versions and passes after; harmless on newer versions where the crash never fired.

Fixes #246.