Slimmable interface and SlimmableContainer

[jfsantos]

1. Slimmable interface on DSP base class (NAM/dsp.h)

Added virtual void SetSlimmableSize(const double val) to DSP. Default is a no-op. val ranges from 0.0 (minimum size) to 1.0 (maximum size).
Subclasses override this to reduce computational cost in a model-specific way.

2. ContainerModel (NAM/container.h, NAM/container.cpp)

A new ContainerModel class that uses the slimmable interface to switch between multiple complete DSP models at different quality tiers.

• Submodel selection: SetSlimmableSize(val) picks the first submodel whose max_value >= val, then always calls ResetAndPrewarm() on it so it's
  immediately ready for process().
• Delegation: process() forwards to the active submodel. Reset() resets all submodels. prewarm() prewarms all submodels.
• Validation (constructor): submodels must be non-empty, sorted by ascending max_value, the last must cover 1.0, and all must agree on sample rate.
• Registration: auto-registered as "SlimmableContainer" architecture via ConfigParserHelper.

The NAM file format nests full model specs inside config.submodels[].model, with an empty top-level weights array.

3. Example file (example_models/slimmable_container.nam)

A 3-tier container using lstm.nam (small, max_value=0.33), wavenet.nam (medium, max_value=0.66), and nano_relu.nam (large, max_value=1.0).

4. Tests (tools/test/test_container.cpp, wired into tools/run_tests.cpp)

10 tests covering:

• Loading from JSON and from .nam file
• Audio processing produces finite output
• SetSlimmableSize selects different submodels (verified by differing output)
• Boundary value selection (exact max_value thresholds)
• Default active model is the largest (max size)
• Error cases: empty submodels, last max_value < 1.0, unsorted submodels, sample rate mismatch

Developed with support and sponsorship from TONE3000

[jfsantos]

Integration tests failed for some reason but that seems to be unrelated to anything I implemented here. Investigating.