chore: Make memory traces clearer

[bhelx]

If you look at the memory traces it's not really clear what the values are:

extism_runtime::memory TRACE 2023-01-23T10:05:16.918413-06:00 - store_u64: 656c626169726176 at offset 25
extism_runtime::memory TRACE 2023-01-23T10:05:16.918418-06:00 - store_u8: 20 at offset 33
extism_runtime::memory TRACE 2023-01-23T10:05:16.918423-06:00 - store_u8: 76 at offset 34
extism_runtime::memory TRACE 2023-01-23T10:05:16.918428-06:00 - store_u8: 61 at offset 35
extism_runtime::memory TRACE 2023-01-23T10:05:16.918433-06:00 - store_u8: 6c at offset 36
extism_runtime::memory TRACE 2023-01-23T10:05:16.918438-06:00 - store_u8: 75 at offset 37
extism_runtime::memory TRACE 2023-01-23T10:05:16.918443-06:00 - store_u8: 65 at offset 38

It's hard to tell that the value is hex and the offset is base10. This changes u8 values to the form 0x00 where there is always 2 digits and it will always use 16 digits for u64.

[bhelx]

it's 04 instead of 02 because rust includes the 0x characters in the max width.