Remove the following attributes and use panic! once we bump MSRV greater than 1.57

• #[allow(unconditional_panic)]
• #[allow(clippy::let_unit_value)]
• #[allow(clippy::out_of_bounds_indexing)]

There are two instances:

• rust-bitcoin/bitcoin/src/blockdata/weight.rs

  Line 65 in 8efaf4a

  None => {

• rust-bitcoin/units/src/amount.rs

  Line 722 in 8efaf4a

  None => {