An invalid ttl raises CacheXError in @cache but TypeError/ValueError in backends and CacheManager

[allen0099]

Problem

An invalid ttl raises different exception types depending on where it is passed:

• @cache(ttl=...) raises CacheXError;
• backends and CacheManager (validate_ttl) raise TypeError or ValueError.

Code that validates user-supplied TTLs has to catch all three.

Proposal

Pick one convention. For example, a CacheXError subclass that also inherits from TypeError / ValueError, so existing except clauses keep working. Document it in the API reference.