Add tokenRefreshLeeway for early access‑token refreshes

[nandan-bhat]

Changes

• Added tokenRefreshLeeway (seconds) to Auth0Client config.
• getAccessToken now refreshes when a token is within the leeway window and a refresh token is available.
• Tests cover early refresh, no‑refresh outside leeway, missing refresh token cases, and invalid config.

Fixes

• Make access token refresh configurable #2428

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.26%. Comparing base (7a15b30) to head (a21a87f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2508      +/-   ##
==========================================
+ Coverage   91.22%   91.26%   +0.04%     
==========================================
  Files          39       39              
  Lines        4705     4718      +13     
  Branches      987      998      +11     
==========================================
+ Hits         4292     4306      +14     
+ Misses        407      406       -1     
  Partials        6        6              

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