Replace BtreeAllocatorTest with individual test cases for copy/move/swap propagation (defined in test_allocator.h) and minimal alignment.

Also remove some extraneous value_types from typed tests. The motivation is to reduce btree_test compile time.

PiperOrigin-RevId: 567376572
Change-Id: I6ac6130b99faeadaedab8c2c7b05d5e23e77cc1e