enhancement: full anyhow::Result<()> support in indexers

[lostman]

Description

Closes #1409.

This PR changes the indexer macro to allow writing functions with a Result type and adds a mechanism to extract the error message from the WASM module. This is done the same way as with panic hook—by storing the message in a static mut String.

The error message automatically includes the block height as well as the name of the failing handler. Multiple errors from multiple handlers can be reported at once.

Testing steps

Deploy an indexer that returns an Err:

use anyhow::Context;

#[indexer(manifest = "examples/fuel-explorer/fuel-explorer/fuel_explorer.manifest.yaml")]
pub mod explorer_index {

    // Returns Result
    fn index_block_3(_block_data: BlockData) -> Result<(), String> {
        Err("Bleep Bleep. Error. Bleep.".to_string())
    }

    // Or anyhow::Result
    fn index_block_2(block_data: BlockData) -> anyhow::Result<()> {
        index_block_2_inner(&block_data).with_context(|| {
            format!("failed at height {}", block_data.height)
        })
    }

    // Returns ()
    fn index_block(block_data: BlockData) {
        // stays the same
    }
}

Check the status:

cargo run -p forc-index -- status

It should display the error, and the context:

✅ Successfully fetched service health:

client status: OK
database status: OK
uptime: 2m 36s

Indexers:

─ fuellabs
   ├─ explorer
   |  • id: 107
   |  • created at: 2023-10-19 19:23:02.325661 UTC (4days 50m 11s ago)
   |  • status: error
   |  • status message:
   |      At height 1:
   |          index_block_3 failed with an error: Bleep Bleep. Error. Bleep.
   |          index_block_2 failed with an error: failed at height 1
   |
   └─ hello_world
      • id: 99
      • created at: 2023-10-17 16:06:58.930780 UTC (6days 4h 6m 14s ago)
      • status: running
      • status message:
          Indexed 940840 blocks

Please provide the exact testing steps for the reviewer(s) if this PR requires testing.

Changelog

• Change the codegen to allow the handler function to either return () or Result type