[API] - make logboek.Context(ctx) safe (avoid panic)

[atlet99]

Problem

Context(ctx) panics when the logger is not stored in the context, which can crash libraries that rely on fallback behaviour.

Proposed Behaviour

Return DefaultLogger() and an error (or boolean) instead of panicking, or provide a helper MustContext() that panics while Context() is safe.

Tasks:

• Decide the preferred API (breaking change? => semver bump).
• Update call-sites & tests.
• Document the change in README.md and doc.go.

[atlet99]

I decide to use next main_test.go for easily testing my ideas:

package logboek

import (
    "context"
    "testing"
)

func TestContext_NoLoggerFallback(t *testing.T) {
    t.Run("background", func(t *testing.T) {
        if got := Context(context.Background()); got != DefaultLogger() {
            t.Errorf("expected DefaultLogger for background ctx")
        }
    })

    t.Run("nil", func(t *testing.T) {
        if got := Context(nil); got != DefaultLogger() {
            t.Errorf("expected DefaultLogger for nil ctx")
        }
    })
}

func TestContext_WithLogger(t *testing.T) {
    custom := NewLogger(OutStream(), ErrStream())
    ctx := NewContext(context.Background(), custom)

    if got := Context(ctx); got != custom {
        t.Errorf("expected custom logger from context")
    }
}

func TestMustContext(t *testing.T) {
    custom := NewLogger(OutStream(), ErrStream())
    ctx := NewContext(context.Background(), custom)

    if got := MustContext(ctx); got != custom {
        t.Errorf("expected custom logger from MustContext")
    }

    cases := []struct {
        name string
        ctx  context.Context
    }{
        {"background", context.Background()},
        {"nil", nil},
    }

    for _, tc := range cases {
        t.Run(tc.name, func(t *testing.T) {
            defer func() {
                if r := recover(); r == nil {
                    t.Errorf("expected panic for %s", tc.name)
                }
            }()
            _ = MustContext(tc.ctx)
        })
    }
}