feat: export of type definitions

[yutak23]

This ought to fix https://github.com/softonic/axios-retry/issues/159.

The intent of this change is detailed in the issue. https://github.com/softonic/axios-retry/issues/159#issuecomment-1809406232

The following tests were performed to verify that axios-retry is available for all patterns.

• JS
  • CommonJS PJ
  • ES Module PJ
• TS
  • CommonJS PJ
  • ES Module PJ

environment

• Node.js v18.17.0
• TypeScript ^5.2.2
• tsconfig.json is below

  {
  "extends": "@tsconfig/node16/tsconfig.json", // @tsconfig/node16: 16.1.1
  "compilerOptions": {
      "strict": true,
      "allowUnusedLabels": false,
      "allowUnreachableCode": false,
      "exactOptionalPropertyTypes": true,
      "noFallthroughCasesInSwitch": true,
      "noImplicitOverride": true,
      "noImplicitReturns": true,
      "noPropertyAccessFromIndexSignature": true,
      "noUncheckedIndexedAccess": true,
      "noUnusedLocals": true,
      "noUnusedParameters": true,
      "checkJs": true,
      "esModuleInterop": true,
      "skipLibCheck": true,
      "forceConsistentCasingInFileNames": true,
      "declaration": true
  },
  "include": ["srv/**/*.ts"],
  "exclude": ["node_modules", "build"]
  }

[yutak23]

Since the branch name is inappropriate, close it and reopen another PR.