fix: replace DOM globals and with inline types in models.ts

[amitsingh05667]

Summary

• src/lib/models.ts used RequestInfo and RequestCredentials as global types without importing them
• These globals come from lib.dom.d.ts (browser library) which is not available in all TypeScript environments
• Users building Node.js backends with "lib": ["es2022"] (no "dom") hit 6 TypeScript compilation errors
• Replaced DOM global aliases with their inline equivalents — structurally identical, no breaking changes

Problem

When a user sets "lib": ["es2022"] in their tsconfig.json, TypeScript does not load DOM types.
RequestInfo and RequestCredentials are DOM globals - they don't exist in this environment, causing compilation to fail.

node_modules/auth0/dist/cjs/lib/models.d.ts:6:36 - error TS2552: Cannot find name 'RequestInfo'.
node_modules/auth0/dist/cjs/lib/models.d.ts:60:19 - error TS2304: Cannot find name 'RequestCredentials'.
Found 6 errors in the same file.

Fixes #1081

Changes

src/lib/models.ts

• Replaced URL | RequestInfo → string | URL | Request (5 occurrences)
• Replaced RequestCredentials → "include" | "omit" | "same-origin"

src/lib/runtime.ts

• Replaced URL | RequestInfo → string | URL | Request in fetch method signature

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.42%. Comparing base (97a4419) to head (accf18b).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1323   +/-   ##
=======================================
  Coverage   89.42%   89.42%           
=======================================
  Files         384      384           
  Lines       18246    18246           
  Branches     9047     9047           
=======================================
  Hits        16316    16316           
  Misses       1926     1926           
  Partials        4        4           

Flag	Coverage Δ
alltests	89.42% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/lib/models.ts	100.00% <ø> (ø)
src/lib/runtime.ts	81.98% <100.00%> (ø)

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