consistently use uint64 for Holocene eip-1559 params

[roberto-bayardo]

Description

We were unnecessarily exposing the fact that these parameters were being encoded as uint32. Changing to always use uint64 outside of the encode/decode abstractions.

[protolambda]

But now the parameters might be corrupted if they're too large. The caller explicitly casting these fixes that, to put the burden on the caller.
Alternatively, maybe add a doc comment about valid range, and assert with a panic the input isn't too large?

[roberto-bayardo]

But now the parameters might be corrupted if they're too large. The caller explicitly casting these fixes that, to put the burden on the caller. Alternatively, maybe add a doc comment about valid range, and assert with a panic the input isn't too large?

good suggestion, done.