refactor(packaging): centralise dependency metadata in pyproject

[ackl]

Hi Robert,

I noticed that there was some redundancy between environment.yml requirements.txt and pyproject.toml, it's possible to just specify everything in pyproject.toml and use that as the source of truth. this way theres less risk of dep versions drifting accidentally if the project updates them in the future.
pip install -r requirements.txt or pip install . or conda env create -f environment.yml all still work exactly as they did before.

MyST has a feature to include files from outside the doc directory, so i've linked docs/installation.md to INSTALL.md, this way there isn't two seprate doc files to maintain for install instructions.

I've also updated the install docs to include some instructions for uv which is a quite a nice python package and env manager.

Also the install docs said that nf2 was available to install via conda on the conda-forge channel but it doesn't actually seem to be published?

╰─$ conda install nf2
2 channel Terms of Service accepted
Channels:
 - conda-forge
 - defaults
Platform: osx-arm64
Collecting package metadata (repodata.json): done
Solving environment: failed

PackagesNotFoundError: The following packages are not available from current channels:

  - nf2

Current channels:

  - https://conda.anaconda.org/conda-forge
  - defaults

Please have a look through this PR when you get a chance