feat: added BigInt encoding support and updated the build toolchain

[mdhthahmd]

Description:

This PR adds an opt-in BigInt mode to Sqids, supporting unsigned 64-bit integers from 0n to 2^64 - 1n.

Example

 import Sqids from 'sqids'

  // Number mode (default)
  const numberSqids = new Sqids()

  const numberId = numberSqids.encode([1, 2, 3])
  const numbers = numberSqids.decode(numberId)

  console.log(numberId) // '86Rf07'
  console.log(numbers) // [1, 2, 3]

  // TypeScript error: Type 'bigint' is not assignable to type 'number'
  // numberSqids.encode([1n, 2n, 3n])


  // BigInt mode
  const bigintSqids = new Sqids({ bigint: true })

  const bigintId = bigintSqids.encode([
    1n,
    42n,
    18_446_744_073_709_551_615n, // Maximum unsigned 64-bit integer
  ])

  const bigints = bigintSqids.decode(bigintId)

  console.log(bigintId) // 'NuzBXdKvyGQqDEOc'
  console.log(bigints) // [1n, 42n, 18_446_744_073_709_551_615n]

  // TypeScript error: Type 'number' is not assignable to type 'bigint'
  // bigintSqids.encode([1, 2, 3])

Changes

• Add BigInt encoding and decoding with { bigint: true }.
• Preserve the existing encoding output for safe integers.
• Add mode-specific TypeScript types and input validation.
• Add tests for BigInt round trips, limits, compatibility, and return types.
• Migrate from Yarn/Beemo to pnpm, tsdown, Biome, and Vitest.
• Update the CI, build, and release workflows.