chore(deps): add missing export for models

[eddyfidel]

This change addresses an issue where the OpenSkill model definitions (bradleyTerryFull, bradleyTerryPart, plackettLuce, thurstoneMostellerFull, and thurstoneMostellerPart) were not properly exported, making them inaccessible through standard import paths. The new configuration in the package.json allows users to directly import these models in their projects using different module formats (ES Modules, CommonJS, and TypeScript types).

Change Details:
The exports section in the package.json was updated to include a dedicated path for the models directory:

"exports": {
  ".": {
    "require": "./dist/index.cjs",
    "import": "./dist/index.js",
    "types": "./dist/index.d.ts"
  },
  "./models": {
    "require": "./dist/models/index.cjs",
    "import": "./dist/models/index.js",
    "types": "./dist/models/index.d.ts"
  }
}

This addition ensures that the various models can now be imported using a simplified syntax and are compatible with different module systems. The following import variants can now be used:

1. ES Modules:

   import {
     bradleyTerryFull,
     bradleyTerryPart,
     plackettLuce,
     thurstoneMostellerFull,
     thurstoneMostellerPart
   } from "openskill/models";

2. CommonJS (Require Syntax):

   const {
     bradleyTerryFull,
     bradleyTerryPart,
     plackettLuce,
     thurstoneMostellerFull,
     thurstoneMostellerPart
   } = require("openskill/models");

3. TypeScript Imports:

   import type {
     bradleyTerryFull,
     bradleyTerryPart,
     plackettLuce,
     thurstoneMostellerFull,
     thurstoneMostellerPart
   } from "openskill/models";

Impact:
This enhancement provides a more convenient and modular import path, allowing users to access the rating models independently from the main library, improving usability and maintaining compatibility with various module systems.

[eddyfidel]

Hi @philihp, please when you get a chance review this PR and let me know if I'm missing something or all good, thanks!

[philihp]

Thank you so much for providing this fix! Apologies for the mistake, this is great work :)

[coveralls]

coverage: 100.0%. remained the same
when pulling 4100e8b on eddyfidel:feature/missing-models-export
into 4f78c21 on philihp:main.