Make ProgramError compatible with pinocchio

[kevinheavey]

Problem: solana-program-error and pinocchio define ProgramError enums that are identical except for the BorshIoError variant, which looks like BorshIoError(String) in solana-program-error and is fieldless (just BorshIoError) in pinocchio.

It is going to be a significant source of grief for users to have two almost-identical ProgramError types in their dependency tree. People will accidentally import the wrong one a lot

Solution: make solana_program_error::ProgramError the same as the pinocchio one so pinocchio can replace its definition with a re-export.

Breaking changes:

• the BorshIoError variants of ProgramError and InstructionError become fieldless. This will require a major version bump for solana-program-error, solana-instruction-error, solana-program and solana-sdk. I haven't included the version bump in the PR as it breaks compilation because of the solana-system-interface dep. This may or may not be curable with patching but is ultimately not a real problem.
• add a num-traits feature to solana-program-error so that all functionality requiring num-traits becomes optional (pinocchio isn't using this functionality)
• make std optional in solana-program-error as pinocchio is no-std. The only thing this affects is impl std::error::Error for ProgramError {}

Other changes:

• Extract solana-pubkey-error and solana-instruction-error crates and use them in solana-program-error. This is so pinocchio's deps can be as light as possible
• Make num-traits optional

[kevinheavey]

CI error is as expected given the breaking change