[Builtin] Tests for memet + few fixes with integer bounds

src/plugins/builtin/memset.ml

src/plugins/builtin/tests/functions/memset_0.c

src/plugins/builtin/tests/functions/memset_FF.c

src/plugins/builtin/tests/functions/memset_value.c

...lugins/builtin/tests/functions/oracle/memset_0.res.oracle

...ugins/builtin/tests/functions/oracle/memset_FF.res.oracle

...ns/builtin/tests/functions/oracle/memset_value.res.oracle