Hotfix/bicgstab null

[maddyscientist]

Hotfix PR that fixes the issue raised in #1532.

• Avoid use of std::swap between x and y vectors as this is buggy
  • the owning vector containers still point to the original objects and so become invalid 🤮 )
• When using initial guesses, the solution vector needs to be zeroed after residual has been computed
• Remove redundant zeroing when fields are first allocated (any required zeroing is handled when solver is applied)

I've cherry picked the changes that allow GitHub actions to continue to work from #1497, as I assume this PR may be merged first.

[weinbe2]

This looks great to me, awesome work @maddyscientist

Of note, as part of testing this I uncovered a few issues triggered by ctest that are unrelated to this PR; I'll file a separate issue for it momentarily.