refactor: replace context.Background() with t.Context()/b.Context() in tests (#7352)

Based on the Go version we currently use, the dependency already
supports 1.24+, which allows using `t.Context()` and `b.Context()` in
unit tests and benchmarks respectively.

- Enable `context-background` and `context-todo` in
[`usetesting`](https://golangci-lint.run/docs/linters/configuration/#usetesting)
- Adjust the code to support linter detection

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
Co-authored-by: Tyler Yahn <codingalias@gmail.com>
Co-authored-by: Damien Mathieu <42@dmathieu.com>

log/logtest/example_test.go

@@ -4,7 +4,6 @@
 package logtest_test
 
 import (
-	"context"
 	"testing"
 	"time"
 
@@ -26,7 +25,7 @@ func Example() {
 	r.SetBody(log.StringValue("Hello there"))
 	r.AddAttributes(log.String("foo", "bar"))
 	r.AddAttributes(log.Int("n", 1))
-	l.Emit(context.Background(), r)
+	l.Emit(t.Context(), r)
 
 	// Verify that the expected and actual log records match.
 	want := logtest.Recording{