Bring traditional-local to feature parity for built-in model comparisons

[Copilot]

The built-in comparison path was asymmetric: bitnet-b1.58-sharp supported checkpoint round-tripping and runtime inspection surfaces that traditional-local did not. This change closes those gaps so both built-in models can be compared through the same repository workflows.

• Checkpoint parity

  • Add TraditionalLocalCheckpoint with JSON save/load support and round-trip validation.
  • Persist the traditional model’s learned state: token embeddings, output weights, output bias, vocabulary, context window, response settings, and seed.
  • Enable the same “train → save → reload → compare response” workflow already available to the BitNet model.

• Inspection parity

  • Make TraditionalLocalHostedAgentModel implement IInspectableHostedAgentModel.
  • Expose GetTernaryWeightStats() from TraditionalLocalModel so the CLI can inspect both built-in models instead of treating traditional-local as unsupported.
  • Generalize inspection output from BitNet-specific wording to model-neutral Weight sign distribution.

• Training report parity

  • Stop returning placeholder 0/0/0 weight counts from traditional-model training.
  • Populate TrainingReport with real negative/zero/positive counts derived from the trained traditional model state.

• Comparison coverage

  • Add focused tests for:
    • traditional-model checkpoint round-trip preservation
    • traditional-model inspectable weight stats
    • non-placeholder weight distribution in training reports
    • checkpoint round-trip coverage for both built-in models in benchmark-oriented execution tests

• Docs

  • Update usage/visualization docs to reflect that both built-in models now expose the same CLI inspection surface.

using var model = HostedAgentModelFactory.Create("traditional-local", VerbosityLevel.Quiet);

var stats = ((IInspectableHostedAgentModel)model).GetTernaryWeightStats();
// stats now reports real negative / zero / positive counts

TraditionalLocalCheckpoint.Save(((TraditionalLocalHostedAgentModel)model).Model, checkpointPath);
var reloaded = TraditionalLocalCheckpoint.Load(checkpointPath, VerbosityLevel.Quiet);

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[Copilot]

Pull request overview

This PR brings the traditional-local model up to parity with the built-in BitNet model for repo workflows (benchmark comparisons, checkpoint round-tripping, and CLI inspection), so both models can be compared through the same training/visualization surfaces.

Changes:

• Add JSON checkpoint save/load + round-trip validation for TraditionalLocalModel.
• Expose traditional-local weight sign distribution via IInspectableHostedAgentModel and propagate real counts into TrainingReport.
• Update CLI/UI strings + docs to use model-neutral “Weight sign distribution”, and add tests covering round-trips and inspection parity.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/BitNetSharp.Tests/TraditionalLocalCheckpointTests.cs	Adds a checkpoint save/load round-trip test for TraditionalLocalModel.
tests/BitNetSharp.Tests/HostedAgentBenchmarksExecutionTests.cs	Adds cross-model checkpoint round-trip execution coverage for both built-ins.
tests/BitNetSharp.Tests/BitNetModelTests.cs	Verifies non-placeholder weight sign distribution and inspectable stats for traditional-local.
src/BitNetSharp.Core/TraditionalLocalModel.cs	Implements weight sign stats + exports/imports of learned state; populates TrainingReport with real counts.
src/BitNetSharp.Core/TraditionalLocalCheckpoint.cs	Introduces JSON checkpoint serialization + load and validation helpers for traditional-local.
src/BitNetSharp.Core/BitNetVisualizer.cs	Generalizes histogram title to “Weight sign distribution”.
src/BitNetSharp.App/TraditionalLocalHostedAgentModel.cs	Implements IInspectableHostedAgentModel for traditional-local.
src/BitNetSharp.App/Program.cs	Generalizes CLI inspection messaging and histogram title for inspectable models.
docs/usage.md	Updates usage text to reflect inspection parity across built-in models.
docs/training-and-visualization.md	Updates visualization docs to reflect model-neutral signed weight histogram output.