Fix all tests/components that fail with `panic: Log in goroutine after TestXXX has completed`

`logptest.NewTestingLogger` uses the `testing.T` passed to it as the logger output, so if any test/component uses the logger after the test has finished, the call will panic like this:
```
panic: Log in goroutine after TestGenerateProcessorList has completed: 2025-11-05T18:46:23.758Z
```

We need to fix all tests/components that fail with this problem.

The currently know failing tests are:
- [ ] [TestGenerateProcessorList](https://github.com/elastic/beats/blob/0e87812a090a6e5634f2361ed153ebbb2f2b7b40/libbeat/publisher/processing/default_test.go#L43). On `main` the panic been mittigaged using a `logp.NewNopLogger`, however the issue is still there. [8.19 BK failure](https://buildkite.com/elastic/beats-libbeat/builds/22868/steps/canvas?sid=019a5537-1fc0-4bfb-8159-14fba7e6503d#019a554e-27e6-43d1-8d05-100be1d8dc14/193-591), [another failure](https://buildkite.com/elastic/beats-libbeat/builds/23136#019a784a-21b5-48b0-b2d2-85e1d5809ebb/192-561)
- [x] [TestRunnerFactoryWithCommonInputSettings](https://github.com/elastic/beats/blob/0e87812a090a6e5634f2361ed153ebbb2f2b7b40/filebeat/channel/runner_test.go#L223) - failing on main.
- [ ] [TestDurationIsAddedToEvent](https://github.com/elastic/beats/blob/c997509ddba73aaebfdae7751a2fb944b756bbfc/metricbeat/mb/module/wrapper_test.go#L208) - failing [on a branch](https://github.com/elastic/beats/actions/runs/19269913266/job/55095245159?pr=47573#step:3:1179).
- [x] [TestNegativeCases](https://github.com/elastic/beats/blob/3b8b99673e633cb4f4240d12d19709b82e9fa6cb/x-pack/filebeat/input/cometd/input.go#L77) - [BK failure](https://buildkite.com/elastic/beats-xpack-filebeat/builds/24331/steps/canvas?sid=019a834c-dcb7-4cf9-ac14-93294f4be867#019a8361-b7a5-4064-938a-0200e34a3865/7-275)
- [x] [TestSimpleInputConfig](https://github.com/elastic/beats/blob/10c60b7/x-pack/libbeat/management/simple_input_config_test.go#L25) - 8.19 branch, [BK failure](https://buildkite.com/elastic/beats-xpack-libbeat/builds/22571#019a9ce8-f576-43d2-9a95-e83c3f40c663/144-559)

Usually running the tests 10 times is enough to catch the flakiness, for example:
```
cd filebeat/channel
go test -count=10 -run=TestRunnerFactoryWithCommonInputSettings .
```

Start with the listed tests in libbeat/publisher/processing/default_test.go, metricbeat/mb/module/wrapper_test.go, and the other linked test locations, then run the affected package tests repeatedly with `go test -count=10`. Trace uses of logptest.NewTestingLogger and the relevant goroutines. Done means the listed failures no longer panic after their tests complete.

Written by the indexing model from the issue text.