test: added some edge cases in reactionsystem.jl and network_properties.jl

[sivasathyaseeelan]

I have added some edge cases in reactionsystem.jl and network_properties.jl which were not tested before.

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[TorkelE]

Looks good to me, but @isaacsas or @vyudu that are familiar with network properties should probably gave a look as well.

[vyudu]

These tests look good to me too, thanks! Note to self that it'd probably be a good idea to rename ratematrix at some point, since fluxmat is being added it could cause some confusion

[isaacsas]

Thanks @sivasathyaseeelan. I will merge assuming tests pass ok.

[isaacsas]

@TorkelE this seems to be a new test failure that just started on master. Any idea about it?