change(ci): Split checking for cached state disks into its own workflow

[teor2345]

Motivation

We want to check for cached state disks for both mainnet and testnet.

This is part of #6367.

Specifications

https://docs.github.com/en/actions/using-workflows/reusing-workflows#using-outputs-from-a-reusable-workflow

Solution

• Split the cached state disk search into a new reusable workflow
• Call it twice: once for the default network (mainnet), and once for testnet

Related fixes:

• Fix a parameter vars.ZCASH_NETWORK that should prefer inputs.network first

Review

This is a routine CI change.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
  • Does it change concurrent code, unsafe code, or consensus rules?
• How do you know it works? Does it have tests?

Follow Up Work

Use the outputs of the new job to build a cached state on testnet and generate testnet checkpoints in CI.

[teor2345]

This seems to be working as expected for mainnet:

STATE_VERSION: 25
Disk: lwd-cache-main-fb3fec0-v25-mainnet-tip-061314
Disk: zebrad-cache-6556-merge-a2ca4de-v25-mainnet-tip-u-140654
Disk: zebrad-cache-6039-merge-62c8ecc-v25-mainnet-checkpoint-053559

https://github.com/ZcashFoundation/zebra/actions/runs/4813941265/jobs/8571075779#step:6:46

And testnet (which has no disks yet):

STATE_VERSION: 25
No TIP disk found for LWD
No TIP disk found for ZEBRA
No CHECKPOINT found for ZEBRA

https://github.com/ZcashFoundation/zebra/actions/runs/4813941265/jobs/8571075399#step:6:46

[gustavovalverde]

LGTM!