feat: Add FeeParameters to BlockHeader

[PhilippGackstatter]

Add FeeParameters to BlockHeader.

Changes

• Adds a new FeeParameters struct defining the native asset of the chain (in which fees are accepted) and a single base fee to keep it simple - to be extended in later work.
• Updates the sub commitment of the block header to commit to these params. Accordingly, the transaction kernel must be updated as well since it computes the same commitment. Note that the sub commitment now includes an empty word. This is so that the sub commitment consists of an even number of words for use with adv_pipe in the kernel. Later additions to the fee params will occupy these zero values anyway.

These additions to the tx kernel are currently not tested, which is not ideal. However, it's not easily possible to create a custom block header and pass it into a transaction using the existing tools (mock chain, tx context). Most likely it would be good to extend the tx context builder to allow for something like this, but I'll need to think about it a bit more in the larger context of testing. Similar errors like ERR_PROLOGUE_GLOBAL_INPUTS_PROVIDED_DO_NOT_MATCH_BLOCK_NUMBER_COMMITMENT are also not tested, so maybe we should come up with a strategy for this.

closes #1612

[PhilippGackstatter]

Just realized I forgot to validate the native asset ID in the prologue - will add and re-request reviews then.

[bobbinth]

Looks good! Thank you! I left a few small comments inline - but nothing blocking.

[mmagician]

Thanks for the express handling of comments!