The value of the variable remains unchanged (4096 = 2 ^ 12), but using a
bitwise expression provides two benefits:

- follows the same approach used for configuring BLOCK_SIZE

- indicates that a power-of-two value is preferred for this kind of
  constant

This commit adds tests for block size constants. Misconfigured sizes
could lead to overflows or performance issues. While such cases are
expected to be rare or unlikely, it's better to be notified of them
early.