MRG: add version to pyproject.toml

[bluegenes]

(now required)

• ref maturin now requires version in pyproject.toml #560

[ctb]

is this now required by pyo3?

[bluegenes]

Required by maturin, I think. Error this solves:

pip install -e .                                ✔  6268  10:11:54
Obtaining file:///Users/ntward/dib-lab/sourmash_plugin_branchwater
  Installing build dependencies ... done
  Checking if build backend supports build_editable ... done
  Getting requirements to build editable ... done
  Preparing editable metadata (pyproject.toml) ... error
  error: subprocess-exited-with-error
  
  × Preparing editable metadata (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> [5 lines of output]
      💥 maturin failed
        Caused by: `project.version` field is required in pyproject.toml unless it is present in the `project.dynamic` list
      Error running maturin: Command '['maturin', 'pep517', 'write-dist-info', '--metadata-directory', '/private/var/folders/pv/_f7m99kd33782sdc79lfqc300000gn/T/pip-modern-metadata-vl8u3z9a', '--interpreter', '/Users/ntward/miniforge3/envs/branchwater-dev/bin/python3.12']' returned non-zero exit status 1.
      Checking for Rust toolchain....
      Running `maturin pep517 write-dist-info --metadata-directory /private/var/folders/pv/_f7m99kd33782sdc79lfqc300000gn/T/pip-modern-metadata-vl8u3z9a --interpreter /Users/ntward/miniforge3/envs/branchwater-dev/bin/python3.12`
      [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> See above for output.

note: This is an issue with the package mentioned above, not pip.
hint: See above for details.