Add explicit numpy dependency

What does this merge request do and why?

We directly require numpy in our code base hence this needs be explicitly added to Poetry.

❯ rg "import numpy"
promptlib/chunking/chunker.py
3:import numpy as np

promptlib/metrics/metrics.py
4:import numpy as np

tests/promptlib/metrics/test_metric.py
3:import numpy as np

We need to constrain numpy to be < 1.25 to be compatible with apache-beam.

Because no versions of apache-beam match >2.52.0,<2.53.0rc1 || >2.53.0rc1,<2.53.0rc2 || >2.53.0rc2,<3.0.0
 and apache-beam (2.53.0rc1) depends on numpy (>=1.14.3,<1.25.0), apache-beam (>2.52.0,<2.53.0rc2 || >2.53.0rc2,<3.0.0) requires numpy (>=1.14.3,<1.25.0).
And because apache-beam (2.53.0rc2) depends on numpy (>=1.14.3,<1.25.0)
 and apache-beam (2.52.0) depends on numpy (>=1.14.3,<1.25.0), apache-beam (>=2.52.0,<3.0.0) requires numpy (>=1.14.3,<1.25.0).
So, because promptlib depends on both apache-beam (^2.52.0) and numpy (^1.26.2), version solving failed.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• I've ran the affected pipeline(s) to validate that nothing is broken.
• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.