setup: various bugfixes

conda-forge::cxx-compiler has been added as a dependency. This ensures that the project's Cython extensions can be built on Linux systems if the host doesn't already have gcc installed. The error command 'gcc' failed: No such file or directory in pip_install.log is fixed by this PR. Unfortunately the XCode setup procedure is still required on macOS if the host doesn't already have the SDK installed.
While solving the environment for the above changes, Mamba found updates among the other dependencies. This included a build of numpy which was built against mkl instead of openblas. The mkl dependency is quite large and increased the project's installation by a whopping 800mb. I've switched numpy's channel from main to conda-forge where it is dependably built against openblas.
If the host requires a Miniconda installation, the setup will fail on certain Linux operating systems producing the error command not found: conda. This is due to a preamble in ~/.bashrc which prevents it from being sourced from a non-interactive shell, i.e. from within the installation script. As a workaround setup.sh now reads the conda init block from ~/.bashrc and executes it.
One user reported receiving the following warnings in pip_install.log: _Warning: Package 'tiny.cwl.tools' is absent from the `packages` configuration. This was likely related to another problem the user reported, and I haven't been able to reproduce it, but nonetheless I'm updating the packages config to use the package discovery method that setuptools recommends.

This PR contains unmerged changes from issue #310. Please close #316 first. Closes #317

MontgomeryLab / tinyRNA

setup: various bugfixes #318