Reorganize tests and add epoch upgrade test

[ss-es]

This PR:

• Reorganizes tests, creating a new CI test group for epoch tests (tests_6)
• Cleans up some justfile commands, removing a bunch that were too specific. Local testing can now be done with just test <testname> (optionally --nocapture).
• Adds a test for an upgrade to a version enabling epochs, but the test is currently disabled because it fails
• Adjusts the marketplace version in EpochsTestVersions, since we expect to deploy epochs well before the marketplace.

This PR does not:

Key places to review:

[lukaszrzasik]

I think something has changed how tests are run locally. I used to run tests locally like this but now I'm getting an error:

$ just test test_success_with_epochs
echo Running test test_success_with_epochs
Running test test_success_with_epochs
RUST_LOG=warn,hotshot_task_impls=debug cargo nextest run --profile local test_success_with_epochs --lib --bins --tests --benches --workspace
error: no such command: `nextest`

	Did you mean `test`?

	View all installed commands with `cargo --list`
	Find a package to install `nextest` with `cargo search cargo-nextest`
error: Recipe `test` failed on line 59 with exit code 101

[lukaszrzasik]

I've been analysing the reason for the test failures. I think I know why but need to confirm it.