Add jacobian for hydro coupling source term

[pajkosmi]

Proposed changes

Calculate Jacobian for M1 source terms. Also update M1 system to use Imex timestepper.

Upgrade instructions

Code review checklist

• [ ] The code is documented and the documentation renders correctly. Run make doc to generate the documentation locally into BUILD_DIR/docs/html. Then open index.html.
• [ ] The code follows the stylistic and code quality guidelines listed in the code review guide.
• [ ] The PR lists upgrade instructions and is labeled bugfix or new feature if appropriate.

Further comments

[wthrowe]

Please rebase now that #6076 is merged.

[pajkosmi]

Please rebase now that #6076 is merged.

rebased

[pajkosmi]

Ping, I freshly rebased and addressed the reviewer comments.

[wthrowe]

Don't delete the CMakeLists.txt files, or at least the one in src. That's preventing some of the CI checks from running.

[wthrowe]

The CMakeLists.txt files you had before the fixup were fine, you were just missing the calls to add_subdirectory in the parents.

[pajkosmi]

squashed

[wthrowe]

You don't seem to have squashed.

[pajkosmi]

You don't seem to have squashed.

edit: see below and ignore italics: When you say squash, do you mean squash all the fixups into 1 fixup commit (like it is now) or squash the 6 current commits (5 initial commits + 1 fixup commit) into 1 commit?

[pajkosmi]

Regarding my previous comment, now I (think) I understand what you meant by squash. I have squashed the fixup commits into the previous relevant commits and rebased.

[pajkosmi]

Everything has been addressed/rebased, except the ImplicitSourceJacobian.hpp point I need clarification on above.

[pajkosmi]

Comments addressed

[wthrowe]

Looks good. The test timeouts look unrelated to these changes, so don't worry about them. Go ahead and squash in the remaining fixups.

[pajkosmi]

squashed