Add Inspection pattern for ergonomic value retrieval

[mpyw]

Summary

This PR introduces a new Inspection pattern that separates context value retrieval from display logic, providing a more ergonomic and flexible API for working with feature flag values.

Key Changes

• New Inspection[V] struct: Captures the key, value, and whether it was set in a single call to Inspect(ctx). All helper methods (Get, TryGet, GetOrDefault, MustGet, IsSet, IsNotSet) are now available on the inspection result without needing to pass context again.

• New BoolInspection struct: A specialized wrapper for boolean feature flags with Enabled(), Disabled(), and ExplicitlyDisabled() convenience methods.

• fmt.Stringer and fmt.GoStringer support: Both Key and Inspection types now implement these interfaces with package-qualified output for better debugging.

• Breaking change: Removed DebugValue/DebugString methods (replaced by Inspection.String()).

Example Usage

var MaxRetries = feature.NewNamed[int]("max-retries")

// Inspect returns both the value and whether it was set
inspection := MaxRetries.Inspect(ctx)
fmt.Println(inspection)         // "max-retries: 5" or "max-retries: <not set>"
fmt.Println(inspection.IsSet()) // true or false

// All helper methods available without context
value := inspection.GetOrDefault(3)

File Changes

File	Description
feature.go	Added Inspect() method to Key[V], InspectBool() to BoolKey, fmt.GoStringer interface, refactored existing methods to use Inspection internally
inspection.go	New file containing Inspection[V] and BoolInspection structs with all helper methods
feature_test.go	Updated tests, removed obsolete DebugValue tests
inspection_test.go	New comprehensive tests for Inspection functionality

Test Plan

• All existing tests pass
• New tests for Inspection and BoolInspection types
• 100% code coverage maintained
• golangci-lint passes with no issues
• go vet passes

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (f138f17) to head (1a74c26).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #2   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            1         2    +1     
  Lines           81       113   +32     
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+ Hits            81       113   +32     

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

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