feat(core): simplify SignalContainer & add type-safe computedFrom overloads

[rodydavis]

Overview

This PR simplifies the generic API signature of SignalContainer across the reactivity framework and introduces 10 strongly-typed global overloads and Record-tuple extensions for the computedFrom API. These additions ensure type-safety, enhance the DX (developer experience), and modernize the API structure.

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Detailed Changes

1. Core Simplification & Cleanup (packages/signals_core)

• Redundant generic removal: Removed the redundant type parameter T from SignalContainer<Arg, S> (and its constructor helper functions), making the container class much cleaner and less prone to generic parameter noise.
• Imports Cleanup: Removed the unused import '../async/state.dart'; statement from container.dart.

2. Type-Safe computedFrom Overloads & Record Extensions

Introduced strongly-typed overloads and record-tuple extension methods to solve type issues with multi-dependency asynchronous computed signals:

• Overloaded Global Helpers: Implemented computedFrom1 through computedFrom10 which accept individual, strongly-typed ReadonlySignal dependencies and automatically pass type-safe values to their callbacks (e.g., FutureOr<T> Function(A, B, C)).
• Record-Tuple Extensions: Implemented ComputedFromExt1 through ComputedFromExt10 which enable elegant, premium inline bindings directly on Dart Records:

  final s1 = signal(1);
  final s2 = signal('a');
  
  final combined = (s1, s2).computedFrom((a, b) async {
    // a is typed as int, b is typed as String
    return '$a-$b';
  });

3. Package Version Bumps

Updated all pubspec.yaml and CHANGELOG.md files to trigger minor version increases for the affected packages:

• signals_core: 7.0.0 ➔ 7.1.0
• signals: 7.1.0 ➔ 7.2.0
• signals_flutter: 7.1.0 ➔ 7.2.0
• signals_hooks: 7.1.0 ➔ 7.2.0
• signals_lint: 7.0.0 ➔ 7.1.0

4. Tests & Documentation

• Comprehensive Tests: Added comprehensive test cases in a new file packages/signals_core/test/async/computed_from_test.dart to verify all 10 overload levels, record-tuple extensions, reactive recalculation behavior, and value type-safety.
• Auto-generated Documentation: Regenerated all reference docs and Jaspr documentation configurations using dart scripts/generate_docs.dart.

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Verification & Testing Results

1. Unit Tests

All 829 test cases in the test suite passed successfully:

dart test

• Status: All tests passed!

2. Static Analysis

Ran a workspace analysis across the modified packages:

dart analyze

• Status: No issues found!