Prefer using `AssetAmount` instead of `u64` for asset amounts

[PhilippGackstatter]

We have recently introduced AssetAmount, but we're not using it to its full extent yet. A couple of improvements we can make:

• impl From<AssetAmount> for Felt so users can infallibly do this conversion without having to expect.
• We can simplify logic like this then:
  

  protocol/crates/miden-protocol/src/asset/fungible.rs

  Lines 153 to 156 in c46871a

  	pub fn to_value_word(&self) -> Word {
  	Word::new([
  	Felt::try_from(u64::from(self.amount))
  	.expect("fungible asset should only allow amounts that fit into a felt"),

• The FungibleAsset::amount API should return AssetAmount instead of u64 so users can take advantage of the guarantees of AssetAmount. This should have a lot of ripple effects to also convert other APIs that deal with asset amounts to use AssetAmount.
• After PSwap Contract #2636:
  • PswapNote::create_args(account_fill: u64, note_fill: u64) which deals with asset amounts.
  • PswapNote::calculate_output_amount(offered_total: u64, requested_total: u64, fill_amount: u64) -> u64 can use AssetAmount.

These are just examples. We should explore the codebase to see where similar patterns can be improved / simplified.

[VAIBHAVJINDAL3012]

Yes, It would really be helpful and make the process of dealing with asset more easier.
Because most of the developers think in u64, and miss the points that asset_max< u64_max.

I also believe we should add more helper functions in this asset masm too so developers can directly use it.
Like, validation_check if u64 in u32 split form is valid asset_amount or not. I have written this check in pswap masm but would be happy to shift it in asset.
https://github.com/0xMiden/protocol/blob/next/crates/miden-protocol/asm/protocol/asset.masm