slog migration: service layer + subsystem libraries (#40661)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #40540 

# Checklist for submitter

- [ ] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
  - Changes present in previous PR

## Testing

- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Refactor**
* Updated internal logging infrastructure to improve consistency and
maintainability across the application.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

ee/orbit/pkg/scep/scep.go

@@ -150,7 +150,8 @@ func NewClient(opts ...Option) (*Client, error) {
 func (c *Client) FetchCert(ctx context.Context) (*x509.Certificate, error) {
 	// We assume the required fields have already been validated by the NewClient factory.
 
-	scepLogger := logging.NewLogger(slog.New(&zerologSlogHandler{logger: c.logger}))
+	slogLogger := slog.New(&zerologSlogHandler{logger: c.logger})
+	scepLogger := logging.NewLogger(slogLogger)
 	opts := []scepclient.Option{
 		scepclient.WithTimeout(c.timeout),
 		scepclient.WithRootCA(c.rootCA),
@@ -159,7 +160,7 @@ func (c *Client) FetchCert(ctx context.Context) (*x509.Certificate, error) {
 		opts = append(opts, scepclient.Insecure())
 	}
 
-	scepClient, err := scepclient.New(c.scepURL, scepLogger, opts...)
+	scepClient, err := scepclient.New(c.scepURL, slogLogger, opts...)
 	if err != nil {
 		return nil, fmt.Errorf("create SCEP client: %w", err)
 	}

ee/orbit/pkg/scep/scep_test.go

@@ -211,7 +211,7 @@ func StartTestSCEPServer(t *testing.T) *httptest.Server {
 		}
 		logger := logging.NewNopLogger()
 		e := scepserver.MakeServerEndpoints(svc)
-		scepHandler := scepserver.MakeHTTPHandler(e, svc, logger)
+		scepHandler := scepserver.MakeHTTPHandler(e, svc, logger.SlogLogger())
 		r := mux.NewRouter()
 		r.Handle("/scep", scepHandler)
 		server = httptest.NewServer(r)