add(scan): Start scanner gRPC server with zebrad

[arya2]

Motivation

We want the zebrad start command to start the scanner gRPC server.

Closes #8242

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Solution

• Add a spawn_init() fn for the root init() fn in zebra_scan
• Replace the call to ScanTask::spawn() in zebrad start command with the new spawn_init() fn

Testing

• This was for manual testing of the ClearResults and DeleteKeys RPC methods and worked as expected.
• Tests that the scanner RPC server is running, accepts connections, and responds to the GetInfo method.

Review

Anyone can review.

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[oxarbitrage]

This looks really good however i found a bug that i think we should fix.

Zebra crashes if the shielded-scan database is not ephemeral with error:

The application panicked (crashed).
Message:  Opening database "/home/alfredo/.cache/zebra/private-scan/v1/mainnet" failed: Error { message: "IO error: lock hold by current process, acquire time 1707322113 acquiring thread 359173: /home/alfredo/.cache/zebra/private-scan/v1/mainnet/LOCK: No locks available" }. Hint: Check if another zebrad process is running. Try changing the state cache_dir in the Zebra config.

Works fine if the shielded-scan.ephemeral config field is true. This is the reason why the test does not detect this.

I am not sure why this is happening and if it was introduced in this PR but the ephemeral is false by default so we should fix before merging.

[arya2]

Works fine if the shielded-scan.ephemeral config field is true. This is the reason why the test does not detect this.

I am not sure why this is happening and if it was introduced in this PR but the ephemeral is false by default so we should fix before merging.

I think it's because the default 'cache_dir' is the same for zebra-state and zebra-scan's Storage, I added a TODO in the zebra-scan config to add a const generic to `DbConfig' for specifying the default cache_dir.

[oxarbitrage]

I think it's because the default 'cache_dir' is the same for zebra-state and zebra-scan's Storage, I added a TODO in the zebra-scan config to add a const generic to `DbConfig' for specifying the default cache_dir.

I think this is not the case, i tried used different directories and the same error happens. Relevant config parts:

[shielded_scan]
cache_dir = "/home/alfredo/.cache/zebra2"
delete_old_database = true
ephemeral = false
listen_addr = "127.0.0.1:8231"

[shielded_scan.sapling_keys_to_scan]

[state]
cache_dir = "/home/alfredo/.cache/zebra"
delete_old_database = true
ephemeral = false

Starting zebra with:

alfredo@spaceship:~/zebra/pr8241/zebra$ ./target/debug/zebrad -c myconf.toml start

[oxarbitrage]

That worked, thanks again.