Gnd test improvements (#6442)

* gnd: implement transaction receipt support for gnd test

Build mock receipts from block events and attach them to log triggers.
Events sharing the same txHash share a receipt whose logs contains all
their logs in declaration order; events without an explicit txHash each
get a unique auto-generated hash and their own single-log receipt.

Receipts are only attached to logs whose event selector (topic0) matches
a handler that declares receipt: true in the manifest, mirroring
production behaviour where graph-node only fetches receipts from the RPC
for those handlers. The selector is computed using the same normalisation
as graph-node's MappingEventHandler::topic0() to handle the manifest's
indexed-before-type convention (e.g. Transfer(indexed address,...)).

Most receipt fields (gas, from, to, status) are hardcoded stubs; only
receipt.logs reflects the actual test data.

* gnd: fix txHash deserialization in test schema

* gnd: add mock IPFS client for file data source testing

Replaces the dummy IpfsRpcClient with a MockIpfsClient that serves
pre-loaded CID → bytes from a "files" array in test JSON files.
Missing CIDs are reported with a clear error instead of a 60-second
timeout. Also adds IpfsResponse::for_test() helper and documents the
unmocked eth_call timeout in the troubleshooting guide.

* gnd: add mock Arweave resolver for file/arweave data source testing

Introduces `MockArweaveResolver` and the `arweaveFiles` schema field so
`gnd test` can serve pre-loaded Arweave content without hitting the
network. Unresolved tx IDs are collected and reported as a clear test
failure, mirroring the existing IPFS mock behaviour.

* gnd: add file data source tests and split fixture subgraphs

Add IPFS and Arweave file data source test fixtures and split the
monolithic gnd_test fixture into four focused subgraphs:

- token/            ERC20 events, eth_call mocking, dynamic templates
- blocks/           Block handlers (every, once, polling filters)
- receipts/         Transaction receipts (receipt: true handlers)
- file-data-sources/ IPFS and Arweave file data sources

Each fixture is a standalone subgraph with its own schema, mappings,
ABIs, and test JSON files. The Rust test harness is updated to use a
generic setup_fixture(name) helper, with one test function per fixture.

* gnd: trim verbose inline comments in test module

* gnd: replace eth_call cache with mock transport layer

Replace the pre-populated eth_call cache approach with a mock Alloy
transport that intercepts RPC calls at the transport level. This makes
tests exercise the real production code path end-to-end.

- Add MockTransport serving eth_call, eth_getBalance, eth_getCode
- Add TestRuntimeAdapterBuilder to convert PossibleReorg → Deterministic
- Add getBalanceCalls/hasCodeCalls to test JSON schema
- Unmocked RPC calls now fail immediately with descriptive errors
- Disable RPC retries in test mode for fast failure

* gnd: update test docs for mock transport and file data sources

- Document getBalanceCalls and hasCodeCalls mock fields
- Document IPFS and Arweave file data source mocking
- Update architecture section to describe mock transport
- Update troubleshooting for immediate unmocked call errors
- Update known limitations table

* gnd: Separate tests and fix retry count env var value

Signed-off-by: Maksim Dimitrov <dimitrov.maksim@gmail.com>

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Signed-off-by: Maksim Dimitrov <dimitrov.maksim@gmail.com>