An edge case for `length` (#31221)
* An edge case for `length`
Though `length` of `AbstractUnitRange` for `(U)Int` and `(U)Int64` has special cased with checked arithmetic, the `(U)Int128` dosen't and uses generic fallback. Therefore, it overflows for
```julia
julia> r = typemin(Int128):typemax(Int128)
-170141183460469231731687303715884105728:170141183460469231731687303715884105727
julia> length(r)
0
julia> r = typemin(UInt128):typemax(UInt128)
0x00000000000000000000000000000000:0xffffffffffffffffffffffffffffffff
julia> length(r)
0x00000000000000000000000000000000
```
whereas
```julia
julia> r = typemin(Int64):typemax(Int64)
-9223372036854775808:9223372036854775807
julia> length(r)
ERROR: OverflowError: 9223372036854775807 -y overflowed for type Int64
Stacktrace:
[1] throw_overflowerr_binaryop(::Symbol, ::Int64, ::Int64) at ./checked.jl:154
[2] checked_sub at ./checked.jl:223 [inlined]
[3] length(::UnitRange{Int64}) at ./range.jl:540
[4] top-level scope at none:0
julia> r = typemin(UInt64):typemax(UInt64)
0x0000000000000000:0xffffffffffffffff
julia> length(r)
ERROR: OverflowError: 18446744073709551615 +y overflowed for type UInt64
Stacktrace:
[1] throw_overflowerr_binaryop(::Symbol, ::UInt64, ::UInt64) at ./checked.jl:154
[2] checked_add at ./checked.jl:166 [inlined]
[3] length(::UnitRange{UInt64}) at ./range.jl:544
[4] top-level scope at none:0
```
I believe this is an inconsistency.
* update StepRange also
* Add `length` tests for edge cases
* Add StepRange tests too
