Cf merger 4: Flash calculations

[vlipovac]

Proposed changes

Extending the compositional subpackage to include the compiled, unified flash.
Includes the Peng-Robinson EoS, its Soereide extension, and some numerical methods (also compiled) required for the flash.

To-do's before converting to PR:

• Include results from last paper as a regression test for the unified flash with Peng-Robinson.
• Tutorial on using the flash.
• Find work-around for numba limitation of defining and passing functions around inside jited functions (modularization of solver and initial guess).
• (optional) Extend flash framework to accept 1-component mixtures (this is highly uncertain as we are dealing with unknown mathematics. In testing phase of some ideas.)

Types of changes

• Minor change (e.g., dependency bumps, broken links).
• Bugfix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• Testing (contribution related to testing of existing or new functionality).
• Documentation (contribution related to adding, improving, or fixing documentation).
• Maintenance (e.g., improve logic and performance, remove obsolete code).
• Other:

Checklist

• The documentation is up-to-date.
• Static typing is included in the update.
• This PR does not duplicate existing functionality.
• The update is covered by the test suite (including tests added in the PR).
• If new skipped tests have been introduced in this PR, pytest was run with the --run-skipped flag.