refactor: Cast type explicitly

[hebasto]

This change:

• Is a pure refactor without altering the assembly code, which might be verified, for example, with the https://godbolt.org/ service.
• Fixes warning C4244 when compiling with MSVC at production quality W3 warning level:

... util\coding.cc(59,18): warning C4244: '=': conversion from 'uint64_t' to 'uint8_t', possible loss of data