SPV workflow for verifying a payment with NiPoPoW

# SPV workflow for verifying a payment with NiPoPoW

Created from ergo-lib [#495](https://github.com/ergoplatform/sigma-rust/issues/495)

Using NiPoPoW described in [KMZ17](https://fc20.ifca.ai/preproceedings/74.pdf)

## Goal
Prove that a payment (ERG and/or tokens) was made on the blockchain.

**EDIT: For a recent payment it would be faster to use UTXO proof described in [#502](https://github.com/ergoplatform/sigma-rust/issues/502)**

## Step 1. Prove that a tx with a given id in a block with a given id exists in the blockchain.

### Step 1.1. Prove that a block with a given id exists in the blockchain.

- 1.1.1. Ask proofs from known nodes via [`/nipopow/proof/{m}/{k}/{headerId}`](https://github.com/ergoplatform/ergo/blob/66ae8ad214e0f56bd8ad39bda0c752fe5a3354a4/src/main/resources/api/openapi.yaml#L2731).

- 1.1.2. Feed all received proofs into [`NipopowVerifier.process()`]( https://github.com/ergoplatform/ergo/blob/66ae8ad214e0f56bd8ad39bda0c752fe5a3354a4/src/main/scala/org/ergoplatform/local/NipopowVerifier.scala#L13-L27).

- 1.1.3. Check that `verifier.bestProof.suffixHead.id` is our block id;

### Step 1.2. Prove that a tx with a given id exists in the blockchain.

- 1.2.1. Ask any node for [`MerkleProof`](https://github.com/input-output-hk/scrypto/blob/88fc0ee4e1eecf3d63e5986487b243b3548bb707/src/main/scala/scorex/crypto/authds/merkle/MerkleProof.scala#L25-L26) via [`/blocks/{headerId}/proofFor/{txId}`](https://github.com/ergoplatform/ergo/blob/66ae8ad214e0f56bd8ad39bda0c752fe5a3354a4/src/main/resources/api/openapi.yaml#L2539-L2570);

- 1.2.2. Confirm the tx id is in the block with [`merkleProof.valid(header.transactionsRoot)`](https://github.com/input-output-hk/scrypto/blob/2237785131ee0946e44d6a5aec2ef0fc0731efce/src/main/scala/scorex/crypto/authds/merkle/MerkleProof.scala#L28-L38);

See Step 1.1 in ergo-lib example [workflow](https://github.com/ergoplatform/sigma-rust/blob/96952de25a34170ba9fea9b1fe533d284dd857e0/bindings/ergo-lib-wasm/tests_browser/test_rest_api.js#L49-L77)

## Step 2. Check the box with the payment

### Step 2.1 Get the whole tx for tx id from Step 1
It can either be provided along with the tx id in Step 1 or fetched from the node. It is verified by serializing the tx and calculating its id and then comparing it to the tx id confirmed in Step 1.2.

### Step 2.2. Confirm the payment is in this tx
Find the output box protected with a certain script (e.g certain PK) and check that its value and/or tokens are as expected.

# Implement the missing parts in appkit:
- REST API calls support mentioned above;
- move `NipopowProof`, `NipopowVerifier`, and all dependent types from node code into a lib ~~(ergo-wallet?)~~ https://github.com/ergoplatform/ergo/issues/1965
- expose `NipopowProof`, `NipopowVerifier`, `MerkleProof` with mentioned above properties/methods in appkit public API.

EDIT: Actually, I'm pretty sure that the above NiPoPoW-related types would better be in a dedicated ergo-nipopow lib since they are not directly related to wallet features. However, the bigger challenge will be the dependent more low-level types like `Header`, etc. Seems like they should be moved to their own separate lib (ergo-core/ergo-chain-types?).

Start with the REST endpoints `/nipopow/proof/{m}/{k}/{headerId}` and `/blocks/{headerId}/proofFor/{txId}`, then review `NipopowVerifier.process()` and `MerkleProof.valid(...)` referenced in the issue. Done would require REST API support and public appkit exposure for `NipopowProof`, `NipopowVerifier`, and `MerkleProof`, while the proposed library boundaries and dependent types still need resolution.

Written by the indexing model from the issue text.