feat!: rework `FullScanRequest` and `SyncRequest`

feat!: rework `FullScanRequest` and `SyncRequest`

Change `FullScanRequest` and `SyncRequest` take in a `chain_tip` as an
option. In turn, `FullScanResult` and `SyncResult` are also changed to
return the update `chain_tip` as an option. This allows the caller to
opt-out of getting a `LocalChain` update.

Rework `FullScanRequest` and `SyncRequest` to have better ergonomics
when inspecting the progress of items of a sync request. Richer progress
data is provided to the inspect closure.

Introduce `FullScanRequestBuilder` and `SyncRequestBuilder`. Separating
out request-construction and request-consumption in different structs
simplifies the API and method names.

Simplify `EsploraExt` and `EsploraAsyncExt` back to having two methods
(`full_scan` and `sync`). The caller can still opt out of fetching a
`LocalChain` update with the new `FullScanRequest` and `SyncRequest`.