Stub in a type for instanbul-lib-report

Adding the local ReportBase stub bridges a gap between the freshly
updated typings and what ships on npm. `@types/istanbul-reports@3.x`
(pulled in transitively by the Jest 30 toolchain) now depends on
`istanbul-lib-report` exposing a `ReportBase` type. However,
`istanbul-lib-report` never published TypeScript definitions, and the
companion `@types/istanbul-lib-report` package on DefinitelyTyped still
targets the old API and does not declare `ReportBase`. Because TypeScript
resolves the `.d.ts` first, the missing export breaks the build:

  npm run build

  > get-azure-pipelines-artifact@0.3.1 build
  > tsc

  node_modules/@types/istanbul-reports/index.d.ts:1:16 - error TS2305:
  Module '"istanbul-lib-report"' has no exported member 'ReportBase'.

  1 import { Node, ReportBase } from "istanbul-lib-report";
                   ~~~~~~~~~~

  Found 1 error in node_modules/@types/istanbul-reports/index.d.ts:1

Until either `istanbul-lib-report` publishes its own typings or the
DefinitelyTyped package is updated, we patch the gap locally with a
minimal augmentation so the compiler can see the symbol and keep the new
Jest stack happy.

Assisted-by: GPT-5-Codex
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

tsconfig.json

@@ -10,6 +10,6 @@
     "noUnusedLocals": true,
     "noUnusedParameters": true
   },
-  "include": ["**/*.ts"],
+  "include": ["**/*.ts", "**/*.d.ts"],
   "exclude": ["node_modules"]
 }

types/istanbul-lib-report/index.d.ts

@@ -0,0 +1,8 @@
+import type { Context as IstanbulContext } from 'istanbul-lib-report';
+
+declare module 'istanbul-lib-report' {
+  export class ReportBase {
+    constructor(options?: { summarizer?: string });
+    execute(context: IstanbulContext): void;
+  }
+}