Raise ConfigException on an out-of-range period value

[eeshsaxena]

Parsing a config whose value is an absurdly large millisecond period crashes with a raw OverflowError:

>>> from pyhocon import ConfigFactory
>>> ConfigFactory.parse_string('a = 99999999999999999999999 ms')
OverflowError: Python int too large to convert to C int

convert_period does int(tokens.value) on an unbounded digit run, and a millisecond period is built with datetime.timedelta, whose C-level day count overflows. Since get_period_expr() is part of value_expr in the parser, this fires at parse time, so any HOCON string containing such a value takes the whole parse down instead of reporting a config error.

The fix catches the overflow in convert_period and raises ConfigException. Normal periods are unaffected. Added a test in tests/test_periods.py.

[eeshsaxena]

Hi! Gentle nudge on this one whenever you have some bandwidth. It's a small, self-contained fix (Raise ConfigException on an out-of-range period value), and it's currently mergeable with no conflicts. No urgency at all, and I'm happy to make any changes you'd like. Thanks for maintaining pyhocon!