ci: ideas for restructuring ci-test

[pro-wh]

• the longest running ones are those that compile rust: test-rust, test-rust-sgx, e2e-ts-web-rt, e2e-rt
• we compile multiple runtimes. maybe we could compile those in separate jobs in parallel, and have those jobs upload the runtimes as artifacts
• has rust's compile cache tooling gotten any better since the last time we tried to use it?
• anything that runs a network runs for a few minutes, with the network needing a few epoch transitions to get started. maybe we could run each test that needs a network in a separate job instead of largely in series