Merge bitcoindevkit/bdk#1216: Migrate to bitcoin::FeeRate

475a77219a6e7649c91b7cfeb44871cee9d0f374 refactor(bdk)!: Remove trait Vbytes (vmammal)
0d64beb040e885d653adb901dc49482f9daafddf chore: organize some imports (vmammal)
89608ddd0fd582d011f7b7ae8bbeb63dee6a3b99 refactor(bdk): display CreateTxError::FeeRateTooLow in sat/vb (vmammal)
09bd86e2d82020d5f4079c5d234888a9eed50489 test(bdk): initialize all feerates from `u64` (vmammal)
004957dc2969171b7a37ce92d2cdb0e8f22b6da5 refactor(bdk)!: drop FeeRate from bdk::types (vmammal)

Pull request description:

  ### Description

  This follows a similar approach to #1141 namely to remove `FeeRate` from `bdk::types` and instead defer to the upstream implementation for all fee rates. The idea is that making the switch allows BDK to benefit from a higher level abstraction, leaving the implementation details largely hidden.

  As noted in #774, we should avoid extraneous conversions that can result in deviations in estimated transaction size and calculated fee amounts, etc. This would happen for example whenever calling a method like `FeeRate::to_sat_per_vb_ceil`. The only exception I would make is if we must return a fee rate error to the user, we might prefer to display it in the more familiar sats/vb, but this would only be useful if the rate can be expressed as a float.

  ### Notes to the reviewers

  `bitcoin::FeeRate` is an integer whose native unit is sats per kilo-weight unit. In order to facilitate the change, a helper method `feerate_unchecked` is added and used only in wallet tests and psbt tests as necessary to convert existing fee rates to the new type. It's "unchecked" in the sense that we're not checking for integer overflow, because it's assumed we're passing a valid fee rate in a unit test.

  Potential follow-ups can include:
  - [x] Constructing a proper `FeeRate` from a `u64` in all unit tests, and thus obviating the need for the helper `feerate_unchecked` going forward.
  - [x] Remove trait `Vbytes`.
  - Consider adding an extra check that the argument to `TxBuilder::drain_to` is within "standard" size limits.
  - Consider refactoring `coin_selection::select_sorted_utxos` to be efficient and readable.

  closes #1136

  ### Changelog notice

  - Removed `FeeRate` type. All fee rates are now rust-bitcoin [`FeeRate`](https://docs.rs/bitcoin/latest/bitcoin/blockdata/fee_rate/struct.FeeRate.html).
  - Removed trait `Vbytes`.

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  evanlinjin:
    ACK 475a77219a6e7649c91b7cfeb44871cee9d0f374

Tree-SHA512: 511dab8aa7a65d2b15b160cb4feb96964e8401bb04cda4ef0f0244524bf23a575b3739783a14b90d2dccc984b3f30f5dabfb0a890ffe7c897c2dc23ba301bcaf