## Why this should be merged
This is a precursor to being able to override `types.Header` RLP
{en,de}coding. As there is already a `Header.EncodeRLP()` method we
either have to modify the generated code or rename the generated
method—this PR does the latter.
## How this works
The `rlpgen -internal_methods` flag changes the generated methods from
`EncodeRLP()` and `DecodeRLP()` to `encodeRLP()` and `decodeRLP()`,
respectively. A new CI job checks that generated code is up to date. We
can then implement our own `Header.EncodeRLP()` that either overrides or
falls back on the original.
It appears that `core/gen_genesis.go` was out of date but only because
of formatting.
## How this was tested
I deliberately excluded the change to `core/types/gen_header_rlp.go` to
confirm that the new workflow
[detects](https://github.com/ava-labs/libevm/actions/runs/12259667481/job/34202386378?pr=86#step:5:92)
the change and fails. The actual change can be inspected via the code
diff.
