update package versions

[mast1ff]

This pull request updates the build tooling and dependencies, modernizes TypeScript and test configurations, and improves compatibility with newer versions of peer dependencies. The main changes involve switching the build system from tsup to tsdown, updating dev dependencies, and making minor code adjustments for better compatibility and maintainability.

Build System & Configuration Updates:

• Replaced tsup with tsdown as the build tool, including adding a new tsdown.config.ts file and removing the old tsup.config.ts. The build script in package.json is updated to use tsdown. [1] [2] [3]
• Updated the biome.json schema version and improved the file inclusion/exclusion patterns for better linting and formatting.

Dependency & Peer Dependency Updates:

• Upgraded several dev dependencies (such as @biomejs/biome, typescript, vitest, and others) to their latest major versions for improved compatibility and features.
• Expanded the supported versions of the zod peer dependency to include both v3 and v4.

Code Compatibility Improvements:

• Changed imports from import { z } from "zod" to import z from "zod" in test files for compatibility with zod v4. [1] [2]
• Updated fetch mocking in test files to use globalThis.fetch instead of global.fetch, ensuring compatibility across environments. [1] [2]
• Removed the fallback for global.fetch in the internal fetch implementation, standardizing on globalThis.fetch.