Align lens documentation with current API defaults and examples

[Copilot]

The lens documentation drifted from the current APIs (defaults, parameter ordering, and example usage). This updates docs to match the updated functions and conventions.

• API reference alignment
  • Updated Lens/GeoLens signatures, defaults, and parameter notes (e.g., sampling counts, wavelength defaults, depth conventions).
• Example correctness
  • Reworked optimization, PSF, and rendering snippets to use current method names and parameter shapes.
  • Removed stale calls and clarified performance/accuracy trade-offs.

Example (updated usage):

params = lens.get_optimizer_params(lrs=[1e-4, 1e-4, 1e-2, 1e-4])
optimizer = torch.optim.Adam(params)

psf = lens.psf(points=[0.0, 0.0, -1000.0], spp=2048)
img_rendered = lens.render(img, depth=-1000)

Original prompt

based on the code edits, check the corresponding project docs, update the documentation if the existing doc doesnot match with the updated functions

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