fix(examples): move the IDR microscopy source to livingobjects.ebi.ac.uk

[emfdavid]

Summary

EMBL-EBI is retiring the uk1s3.embassy.ebi.ac.uk S3 endpoint that the microscopy example's --source idr reads from. The IDR image now lives at livingobjects.ebi.ac.uk, which has the same idr bucket, the same key layout, the same anonymous path-style S3 access, and byte-identical .zarray metadata. The only code change is IDR_ENDPOINT in examples/microscopy/data.py.

Nothing tested the real-IDR path before this PR, so this adds test_idr_store_streams_the_real_image (marked remote). It checks the geometry (236 planes, Z-chunks of 1 and 30), streams one batch, and compares it with a direct zarr read.

Closes #97

For reviewers

The test is only as good as the proof that it reads the live host, so it was run three ways:

• Old endpoint: passes, which shows the test works.
• Nonexistent endpoint (https://nonexistent.invalid): fails with an obstore error, so the test really goes through the endpoint rather than a cache.
• New endpoint: passes.

python -m examples.microscopy.train_torch --source idr --epochs 1 --sample-range 0,120 also runs end to end against the new host.

CI never passes --remote, so CI will skip this test. #100 proposes a weekly scheduled --remote job. The Zarr v3 (OME-NGFF v0.5) version of this image, which the issue mentions, is tracked separately in #99: its layout differs (4-D, sharded, different label path), so it isn't just a URL swap.

Author attestation

• I have reviewed every change in this PR, I can explain why each one is correct, and I
  have verified the claims made in this description.

Checklist

• Tests added or updated. The old endpoint still works, so no test could fail before this change; the bogus-endpoint run above stands in for that failing-first run.
• uv run ruff check src tests bench examples, uv run ruff format --check src tests bench examples, uv run mypy src bench examples and uv run pytest -q are green
  locally (668 passed, 9 skipped; test_tf.py skipped because TensorFlow isn't installed in this env), plus uv run --extra docs mkdocs build --strict
• A bullet added under ## Unreleased in CHANGELOG.md
• No load-bearing invariant is broken

🤖 Generated with Claude Code

[emfdavid]

Thank you @will-moore