std.fmt: add `#` specifier to print raw bytes of the value (hex)

[Vexu]

This was accepted as part of #1358 but never implemented. I'm opening this as a new proposal since it is of questionable usefulness:

(NOTE: do we need this? how often is it used?)

[InKryption]

I don't think it's necessary, if one wants they can use std.mem.asBytes -> std.fmt.fmtSliceHexLower/fmtSliceHexUpper.
Could even make a function in std.fmt like fmtAsBytesUpper, which does the same thing, if verbosity is an issue with that solution (ditto for fmtAsBytesLower).

[matu3ba]

I do agree with @InKryption that it is semantically not necessary and at first would be simpler to do without another flag to std.fmt

• 1. However, it is poorly documented how to get the in-memory representation
• 2. Printing the raw bytes is common on analyzing padding + alignment issues on overlapping types besides bit logic things like int, float, deterministic bigint stuff in buffers etc.
• 3. If I want 5 values next to another like a csv table over time (say with file,line number + iteration), then writing those out will be annoying. How useful or common this is, would be the other question.