October: DB MemoryCache doesn't support Query Expressions

[LukeTowers]

Expected behavior

The memory cache functionality added in https://github.com/octobercms/library/pull/253 should work flawlessly with any query.

Actual behavior

Queries that are built on Illuminate\Database\Query\Expressions via $query->addSelect(new Expression($values)); fail hard with Exception: Illegal offset type in October\Rain\Database\MemoryCache->put() on the $this->tableMap[$query->from][] = $hash; line.

Reproduce steps

Utilize the Searchable Trait on any model and then perform a query that triggers that trait. This will replace $query->from with an Expression object that will not be explicitly cast to string for utilizing as an array key in the MemoryCache implementation.

[LukeTowers]

Fix in progress

[LukeTowers]

Props to @triasrahman for reporting initially.

[LukeTowers]

Fixed in https://github.com/octobercms/library/commit/efbccea74a9f1910a262fd7a5e45e537989e74b1