* chore: eth: move & rename input/output encoding functions
These are shared functions, so I'm moving them to the utils library.
* fix: eth: correctly encode and simplify native input/output encoding
When generating eth traces, we encode "native" message inputs/outputs
to "solidity ABI" by formatting the inputs/outputs the same way we do in
FEVM's "handle_native_method". However, we had quite a few bugs with the
implementation:
1. We were right-aligning 64bit values in 256bit words, instead of
left-aligning (as we should given that these values are big-endian).
2. The return-value encoding wasn't correctly handling lengths.
This patch:
1. Fixes those bugs.
2. Deduplicates the logic (we're doing _basically_ the same thing in
both cases).
3. Removes all error paths (these functions can't fail).
