Fix crash parsing non-finite numbers (inf/nan) in namelists

[jacquelinegarrahan]

Fix crash parsing non-finite numbers in namelists

Branch: bugfix/namelist-nonfinite-numbers → main

Bug

lume/parsers/numbers.py::try_int converts a float to int unconditionally:

def try_int(x):
    if x == int(x):   # int(inf) -> OverflowError; int(nan) -> ValueError
        return int(x)
    else:
        return x

number() routes every float-like token through try_int(float(z)), so any
token that float() accepts but int() cannot convert crashes the parser:

Input	Before	After
"inf"	OverflowError	inf
"-inf"	OverflowError	-inf
"nan"	ValueError	nan
"1e400"	OverflowError	inf

Both single-value (parse_unrolled_namelist line 123) and vector (line 127)
paths call number(), so a namelist file containing e.g. b = Inf — which
appears in real Fortran/Astra/Impact numeric output — crashed the whole parse.
The numbers.py/namelist.py parsers have no test coverage, so this slipped
through.

Fix

Guard the int() conversion in try_int and return the value unchanged when it
is not a finite integer. Integral floats (1.0 -> 1) and strings are unaffected.

Verification

pytest -q                       # 121 passed
number('inf')  -> inf           # (was OverflowError)
number('nan')  -> nan           # (was ValueError)
number('1e400')-> inf           # (was OverflowError)
number('1.5')  -> 1.5           # unchanged
number('1')    -> 1             # unchanged

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