Fix unit tests for the analysis module

[p-j-smith]

Fixes #30

The tests for the analysis module were broken because the module isn't installed in the virtual environment when installing the pyonb package.

• move the analysis module into pyonb.analysis
• update docs to reflect the move

Running pytest tests/analysis/test_eval_ocr.py now passes:

Test output

===================================================== test session starts =====================================================
platform darwin -- Python 3.13.1, pytest-8.4.1, pluggy-1.6.0 -- /Users/paul/git/safehr/pyonb/.venv/bin/python3
cachedir: .pytest_cache
rootdir: /Users/paul/git/safehr/pyonb
configfile: pyproject.toml
plugins: anyio-4.9.0, cov-6.2.1
collected 2 items

tests/analysis/test_eval_ocr.py::test_read_file PASSED                                                                  [ 50%]
tests/analysis/test_eval_ocr.py::test_evaluate_metrics PASSED                                                           [100%]

====================================================== 2 passed in 0.07s ======================================================

[tomaroberts]

Lovely stuff, thanks Paul. Please merge.