Delegate `FeeRate::to_sat_per_vb_ceil` back to rust-bitcoin after the units 1.0 bump

[thunderbiscuit]

#1076 fixes an overflow in FeeRate for fee rates near u64::MAX sat/kwu. The overflow is in rust-bitcoin's bitcoin-units 0.1.x, which rounds up with (sat_kwu + 249) / 250.

To fix it, #1076 stopped calling the upstream code in two places:

• FeeRate::to_sat_per_vb_ceil does its own rounding with self.0.to_sat_per_kwu().div_ceil(250)
• impl Display for FeeRate no longer calls upstream's {:#} formatter. It builds the same "{}.00 sat/vbyte" string itself.

Upstream status

This is fixed on rust-bitcoin master. In bitcoin-units 1.0 (currently 1.0.0-rc.4, used by the bitcoin 0.33 betas), to_sat_per_vb_ceil is implemented with div_ceil and does not overflow.

Todo when we move to bitcoin 0.33.0

• Change FeeRate::to_sat_per_vb_ceil back to calling self.0.to_sat_per_vb_ceil().
• Check whether ExtractTxError::AbsurdFeeRate still needs to convert through crate::bitcoin::FeeRate before calling to_sat_per_vb_ceil, or can call the upstream method directly.
• Keep the regression tests from fix: prevent maximum fee rate overflow #1076 (maximum_fee_rate_converts_and_displays_without_overflow and test_extract_tx_fee_overflow_maps_to_maximum_fee_rate). Update them for the new API if needed, and make sure they still pass.

Notes

• Display stays our own code. FeeRate in bitcoin-units 1.0 has no Display impl, so there is no upstream formatter to call.
• This is a good time to reconsider the format. The current "{}.00 sat/vbyte" always rounds the .00 looks more precise than the value is (for example, 0.1 sat/vB displays as 1.00 sat/vbyte).