Strict mode to fail on CAST timestamp <-> numeric

There is some interest in enforcing that CAST numeric <-> timestamp is disallowed to avoid confusion among users, e.g., SQL standard does not allow numeric <-> timestamp casting, timestamp type is timezone agnostic, etc.

We should introduce a strict config for timestamp (similar to others before): If the config is true, we shall fail while compiling the query with a meaningful message.

To provide similar behavior, Hive has multiple functions that provide clearer semantics for numeric to timestamp conversion (and vice versa):
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-DateFunctions