Stress test parameter groups and fix from_valid bug in multi-group fill_params

[Copilot]

Adds comprehensive test coverage for parameter groups across all major caskade features, and fixes a bug discovered during testing.

Bug fix

fill_params called from_valid(params_g, param_list_g) without passing group=group, causing from_valid to re-enter its multi-group branch and attempt to iterate a single group's tensor as a list of group tensors. This produces an IndexError when using ValidContext with multi-group parameters.

# This would crash before the fix
m = BoundedSim()  # module with valid bounds
m.to_dynamic(False)
m.b.group = 1

with ValidContext(m):
    params = m.get_values()
    m.run(5.0, params)  # IndexError: too many indices for tensor of dimension 0

Fix in module.py:173: pass group=group to self.from_valid().

Test coverage (65 tests)

• Hierarchical models — groups at top-level, within sub-modules, mixed across levels, 3-level deep nesting
• Batch dimensions — independent batch dims per group, different batch sizes across groups, multi-dimensional batch shapes
• get/set values — all three schemes (array, list, dict), specific group retrieval, round-trip consistency
• find_param / find_index — group-aware lookups, error cases
• ValidContext + to_valid/from_valid — multi-group transforms, round-trips, per-group argument
• @forward + fill_params — multi-group param passing (positional and kwarg), single vs multi-group result consistency
• ActiveContext, active_cache, OverrideParam — state management, caching, value overrides with groups
• Collections — NodeList, NodeTuple with grouped params
• Pointer params — shared params across modules with groups
• Dynamic/static transitions — group preservation across state changes, empty group removal
• Edge cases — 10+ groups, non-contiguous group IDs, reassignment collapse, None-value params

Original prompt

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This section details on the original issue you should resolve

<issue_title>Stress test parameter group options</issue_title>
<issue_description>We need to write a more complete unit test suite for parameter groups under a number of edge cases. For example, we should test parameter groups in hierarchical models (both at the top level and within the hierarchy). It would also be good to test groups with varying batch dimensions, the batch dims of two separate groups should be independent. Parameter groups should be tested against basically all other features of caskade to make sure everything runs smoothly.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Stress test parameter group options #83

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (8de9229) to head (d35d518).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #84   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           13        13           
  Lines         1617      1617           
=========================================
  Hits          1617      1617           

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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