Fix all LA memory leaks forever!

Bug: 27072626

Or at least fix this one and make it harder to leak
going forward. static_asserts are cool, use them liberally

Also makes allocation via LA (slightly) faster by fixing create*
variants to use rvalue references & std::forward, preventing
an accidental pass-by-value

Change-Id: I18fd696a93dd6ea49c8d8c587d4c8bee56dbfdf5