artificial trace_pc instruction to print instruction's address

[kvpanch]

No description provided.

[koute]

LGTM, just need to fix failing CI.

[koute]

Hmm... actually, (optional) suggestion: you're currently allocating two strings per trace_pc invocation, which is going to be slow (and this is a trace log which will run per instruction, so it's going to be extremely spammy, so the speed difference will matter). But there is a way to avoid allocations: define a struct, shove all of the data you need into it, and implement Display for it, and then you can print it out without any allocations.

For example, take a look at e.g. format_jump/format_imm or any other Display impl in polkavm-common/src/program.rs. Over there instead of returning a String (hence triggering an allocation) I return a struct implementing Display, and that can be directly printed.