RPC wallet syncing example with Functional tests

[rajarshimaitra]

This PR adds the complete RPC syncing example with functional tests added in bdk_rpc_wallet_example/tests.

The RPC sync is by the "import into a core wallet" approach.

The functional tests covers 3 basic tests

• Basic sync
• Basic reorg situation
• Sending transactions.

This can be used as a reference to use the bitcoind backend to run similar electrum and esplora functional tests.

More tests would be added in this PR or later.

[codecov-commenter]

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[rajarshimaitra]

The latest update does the following:

• Fix the failing tests.
• Adds docs and comments.
• Merge all the RPC and tests commits together.
• Overrides Add a RPC syncing example. #79 .

[LLFourn]

Thanks @rajarshimaitra. I think the design works. I suggest trimming down the scope of rpc.rs to only wallet_scan. Everything else seems like pure example code that can go in main.rs. The user can be left to make sure that all the spks they are interested in are loaded into the wallet. This allows them to use descriptors also. If we want to get more opinionated about this we can do it later.

The tests are not testing wallet_scan. I think they should only be testing the sparse chain output from wallet_scan.

I think we should make use of the label feature in bitcoin core rpc so wallet_scan takes a label to scan over (perhaps optional). In the example we should somehow expose the label.

Maybe call wallet_scan fetch_sparse_chain.

[rajarshimaitra]

Thanks @LLFourn for the review.. Updated as suggested.

• Helper functions moved to main.rs.
• wallet_sync moved to lib.rs.
• Couldn't remove the struct RpcClient as bdk_cli::handle_commands expect a generic trait bound Broadcast and we can't impl foreign traits on foreign types.
• Blockchain tests only testing for sparsechain structure.
• We can't do create transaction test if we aren't fully syncing the tracker, which is the case currently as we are only getting the update_sparsechain from wallet_sync.

[LLFourn]

Thanks @rajarshimaitra.

* Helper functions moved to `main.rs`.

* `wallet_sync` moved to `lib.rs`.

* Couldn't remove the struct `RpcClient` as `bdk_cli::handle_commands` expect a generic trait bound `Broadcast` and we can't impl foreign traits on foreign types.

We could fix this by getting rid of the Broadcast trait and just passing in a closure to the cli lib's main handler that takes a tx and broadcasts it. See #198

* Blockchain tests only testing for sparsechain structure.

* We can't do create transaction test if we aren't fully syncing the tracker, which is the case currently as we are only getting the `update_sparsechain` from `wallet_sync`.

This is good because this library doesn't provide create tx functionality.

[rajarshimaitra]

We could fix this by getting rid of the Broadcast trait and just passing in a closure to the cli lib's main handler that takes a tx and broadcasts it. See #198

That totally makes sense.. Will update accordingly.. Should I just build this over #198 or port the change?