Custom error decoder

[CriesofCarrots]

Problem

The solana-sdk offers an easy way to encode custom program instruction errors (into InstructionError::CustomError(<u32>)), but no easy way to decode them.

Summary of Changes

Add DecodeError trait to solana-sdk
Impl DecodeError for relevant solana native programs
Plumb through wallet to log and return decoded custom errors

FYI, @rob-solana

[CriesofCarrots]

There's a clippy error in the num_derive crate (rust-num/num-derive#20). Because it's in a proc macro, it can't be narrowly ignored. There's a fix coming in clippy (rust-lang/rust-clippy#3932), but it hasn't landed yet, and it doesn't look like it's in Rust-1.34 clippy either.
... hence the ugly, module-level ignores.
On pr merge, will file issue to track and improve.

[codecov]

Codecov Report

Merging #3783 into master will decrease coverage by 0.1%.
The diff coverage is 39.5%.

@@           Coverage Diff            @@
##           master   #3783     +/-   ##
========================================
- Coverage    77.6%   77.5%   -0.2%     
========================================
  Files         162     164      +2     
  Lines       27737   27806     +69     
========================================
+ Hits        21533   21552     +19     
- Misses       6204    6254     +50

[mvines]

oops, I didn't see this review request until now. looks great

[CriesofCarrots]

There's a clippy error in the num_derive crate (rust-num/num-derive#20). Because it's in a proc macro, it can't be narrowly ignored. There's a fix coming in clippy (rust-lang/rust-clippy#3932), but it hasn't landed yet, and it doesn't look like it's in Rust-1.34 clippy either.
... hence the ugly, module-level ignores.
On pr merge, will file issue to track and improve.

Update: num_derive is fixed, woot! Rebased and removed the ugly clippy fix :)