fix: hb_maps:get defaults and defaults validation

[charmful0x]

addressed #688 (comment) in a separate PR due to wider scope

TLDR

there was mixed hb_maps:get/3 and hb_maps:get/4 usage where some get/3 calls passed Opts as the default value instead of using arity 4 -- patched in:

• dev_pot_test_vectors
• dev_mint_math
• dev_mint_stats

also added a fail fast hb_util:safe_int/1 wrapper (dev_mint_math:required_int/1) to replace previous hb_util:int/1 usage on required numeric fields, so failures now throw typed errors instead of generic crashes (as the get/4 defaults are now correctly in place)

%% @doc Fail Fast wrapper for hb_util:safe_int.
required_int(Value) ->
    case hb_util:safe_int(Value) of
        {ok, SafeInt} -> SafeInt;
        _ -> throw({error, required_int_parse_failure})
    end.

tests run:

rebar3 eunit --module=dev_mint_test_vectors
rebar3 eunit --module=dev_pot_test_vectors
rebar3 eunit --module=dev_pot_math_props
rebar3 eunit --module=dev_pot_props