`bdk`: add `BDKError` into `WalletError`

[wthrajat]

Aims to fix https://github.com/citadel-tech/coinswap/issues/202

[KnowWhoami]

It doesn't include BDKStore specific errors :

• InvalidMagicBytes : which is returned while opening a bdk_store https://github.com/bitcoindevkit/bdk/blob/d99b3ef4b449a5c7b8facf04db3cb9be829a0ac1/crates/file_store/src/lib.rs#L20

• https://github.com/bitcoindevkit/bdk/blob/d99b3ef4b449a5c7b8facf04db3cb9be829a0ac1/crates/file_store/src/store.rs#L187

• IterError : used in AggregateChangesetsError https://github.com/bitcoindevkit/bdk/blob/d99b3ef4b449a5c7b8facf04db3cb9be829a0ac1/crates/file_store/src/entry_iter.rs#L16

since we are only taking care of io::Error in WalletError which is relevant to BDKStore . IMO , there should be dedicated error enum for BDKStore which can take up all these specific errors. which must be included in BdkError.

[mojoX911]

For now its okay to just put them in BdkError. If they become very large, we can take them out in a separate enum in future.

[KnowWhoami]

For now its okay to just put them in BdkError. If they become very large, we can take them out in a separate enum in future.

this is already solved in #178