Revise SVS_CHECK_BOUNDS logic

[ethanglaser]

• Refactors SVS_CHECK_BOUNDS logic so that explicitly passing SVS_EXPERIMENTAL_CHECK_BOUNDS will trump any other settings, but not explicitly passing will lead to SVS_CHECK_BOUNDS depending on CMAKE_BUILD_TYPE
• Previously, non-Release builds would force bounds checking on even when a user explicitly passed -DSVS_EXPERIMENTAL_CHECK_BOUNDS=OFF, but this now changes - see table below for more details
• Updates docs to reflect the conditional default

SVS_CHECK_BOUNDS value (current behavior)

SVS_CHECK_BOUNDS value (updated behavior)