change(consensus): Build Sprout and Sapling parameters into the zebrad binary, so a download server isn't needed

[teor2345]

Motivation

We don't want to rely on a single external download server when Zebra first runs.

Close #7613
Close #6963

Fixes known issue in README with parameter downloads
Reduces the size of the full Zebra install and cache on disk by 700 MB (we don't need the full Sprout parameters any more)

This PR series will eventually:

• Simplify CI and makes it more reliable
• Remove unnecessary code and tests from Zebra

Specifications

This PR is based on the corresponding zcashd PR zcash/zcash#6661

Complex Code or Requirements

Loading bytes from inside the binary is much simpler, as long as our build disks are large enough. (The final size is smaller because we drop the sprout prover and transcript from the build and binaries.)

Solution

Production code:

• load sapling parameters from inside the binary
• load sprout parameters from inside the binary
• remove parameter download code and dependency features
• reword log messages and documentation (partial)

CI and testing:

• remove download examples
• remove workflow steps that download parameters

Documentation:

• add a changelog entry based on zebrad's changelog entry

Testing

We have existing comprehensive tests for the Sprout and Sapling parameters. Sapling is tested regularly by our integration and sync tests.

Sprout might not be tested, so

Review

This is a routine change, but it is blocking cleanup work in other PRs.

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?

Please manually check that the new sprout file contains the correct data. Here is how the zcashd team did it:
https://github.com/zcash/zcash/pull/6661/files#r1248159359

[teor2345]

rpc_endpoint_parallel_threads failed with a timing issue, we might want to fix that test to use the logs rather than a fixed time.

https://github.com/ZcashFoundation/zebra/actions/runs/6607410396/job/17944979809?pr=7800#step:4:6196

This is unrelated and will be cleared the next time I push.