Add devel/p5-Data-Lock, a facility to mark variables as immutable. It is
comparable to p5-Readonly (but much faster; see
https://metacpan.org/pod/Data::Lock#BENCHMARK), or to the constant
pragma (except it retains sigils). It includes Data::Lock and its
dlock() function which handles scalars, and Attribute::Constant which
exports a ': Constant' attribute, which is faster but has caveats.