feat: added a slug-prefix parameter for link anchors

Motivation: when using a matrix job, or more than one kind of tests in a same workflow, we can end up with multiple summaries at the same time. This will lead to multiple anchors and html id that will no longer be unique.
This prefix option allow to disambiguate those anchors ; and keep them functional.

__tests__/utils/slugger.test.ts

@@ -0,0 +1,28 @@
+import {DEFAULT_OPTIONS} from '../../src/report/get-report.js'
+import {slug} from '../../src/utils/slugger.js'
+
+describe('slugger', () => {
+  it('adds prefix from report options to generated slug', () => {
+    const result = slug('r0s1', {
+      ...DEFAULT_OPTIONS,
+      slugPrefix: 'prefix-'
+    })
+
+    expect(result).toEqual({
+      id: 'user-content-prefix-r0s1',
+      link: '#user-content-prefix-r0s1'
+    })
+  })
+
+  it('sanitizes custom prefix using existing slug normalization', () => {
+    const result = slug('r0', {
+      ...DEFAULT_OPTIONS,
+      slugPrefix: ' my /custom_prefix?.'
+    })
+
+    expect(result).toEqual({
+      id: 'user-content-my-customprefix-r0',
+      link: '#user-content-my-customprefix-r0'
+    })
+  })
+})