Bound SEA auth retry counts

[ming1523]

Summary

• normalize SEA auth retry counts to finite non-negative integers
• preserve the default retry budget and retries=0 behavior
• add regression coverage for default, zero, one, negative, fractional, and infinite values

Validation

• node --check sea.js
• node --check sea/auth.js
• node --check test/sea/sea.js
• direct auth control-flow smoke test: all six cases completed with an error callback
• npm run testsea -- --grep "auth retry bounds" could not start because mocha is not installed in the environment