Refactor adapters to share and reuse common code

[ChristopherHogan]

There is a lot of duplicated code in the stdio, POSIX, and MPI-IO adapters. We need a common adapter layer that each adapter can inherit so we're not repeating ourselves so much.

Goals

• [ ] Reduce code duplication.
• [ ] Reduce test runtime while maintaining the same coverage.
• [ ] Reduce log size without sacrificing information
• [X] Reduce the number of directories. Done in #315
• [x] Make it easier to tell which specific test failed in the logs by adding -d yes to all Catch2 tests