[PB-6601]: feat/add-token-refresh-functionality

[larryrider]

Adds JWT expiration/refresh logic to @internxt/lib's auth module, so any consuming project (CLI, drive-web, etc.) can share a single source of truth instead of re-implementing this logic per repo.

Public API surface is intentionally kept small, only the two functions consumers actually need:

• checkTokenExpiration(expirationTimestamp, issuedAtTimestamp) -> returns a TokenStatus. Refresh is required once the token has consumed 50% of its lifetime (exp - iat) and it falls back to a fixed 6-hour margin when iat is not available.
• validateTokenAndCheckExpiration(token) -> decodes a raw JWT string and returns the same TokenStatus directly (but INVALID if the token is malformed/unparseable).

export enum TokenStatus {
INVALID = 'INVALID',
EXPIRED = 'EXPIRED',
REFRESH_REQUIRED = 'REFRESH_REQUIRED',
VALID = 'VALID',
}
The lower-level building blocks (isTokenExpired, isTokenRefreshRequired, validateJwtAndCheckExpiration) remain exported from their own modules (not re-exported through the auth namespace) for potential future granular use, but are not part of the current public API.

**I have also migrated the project from yarn to npm as we are doing on all internxt projects progressively