fix: dev: Validate -l and -L numeric arguments in named-checkzone

named-checkzone and named-compilezone parsed the -l (max TTL) and -L
(source serial) arguments with strtol(), so a negative value such as
-1 silently became UINT32_MAX and out-of-range values were truncated
to 32 bits without warning; -l in particular appeared to cap TTLs but
no longer enforced anything. Both flags now go through isc_parse_uint32()
and reject any value that is not a valid 32-bit unsigned integer.

Merge branch 'ondrej/named-checkzone-strtol-truncation' into 'main'

See merge request isc-projects/bind9!11900