fix(CI): Cache compilation results

[upbqdn]

Motivation

• Close CI recompiles Zebra from scratch for each CI test #9331.

Solution

• Cache downloaded crates between image preparations: https://github.com/ZcashFoundation/zebra/actions/runs/13837431819/job/38722773169?pr=9323#step:10:367 vs https://github.com/ZcashFoundation/zebra/actions/runs/13867297186/job/38808809286?pr=9328#step:10:1.
• Cache compiled crates between image preparations: https://github.com/ZcashFoundation/zebra/actions/runs/13837431819/job/38722773169?pr=9323#step:10:871 vs https://github.com/ZcashFoundation/zebra/actions/runs/13867297186/job/38808809286?pr=9328#step:10:387.
• Cache compiled crates between image preparation and tests: https://github.com/ZcashFoundation/zebra/actions/runs/13837431819/job/38722794636?pr=9323#step:14:146 vs https://github.com/ZcashFoundation/zebra/actions/runs/13867297283/job/38809190703?pr=9328#step:14:134. For this test, the runtime went down from 33 minutes to 13 minutes.
• Unify compilation parameters for all CI tests so caching can kick in.

Clean-ups

• Mount lwd's and Zebra's cached states to implicit locations instead of explicitly specifying the location in each test.

Tests

• CI is noticeably faster.

PR Checklist

• The PR name is suitable for the release notes.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.
• If the PR shouldn't be in the release notes, it has the
  C-exclude-from-changelog label.

[upbqdn]

This PR seems to make CI noticeably faster.

[upbqdn]

We could bring the CI time down to ~25 minutes if we moved these three tests to run only on main:

[upbqdn]

This is a rather awful hack. I think there could a cleaner solution, but I coulnd't come up with anything better.

[conradoplg]

Why is this needed?

[gustavovalverde]

This might be the best context to answer that #6169 (comment)