Checkpoint: Memory & Lifetime

This checkpoint combines the module's skills into one function with an honest contract:

• input is borrowed (const long*, possibly null) — never copied, never freed
• the count is validated — invalid input throws, it is not silently ignored
• the cap bounds the result — early exit is part of the spec, not a hack

Write bounded_total so all four tests pass, then compare with the reference: notice there is no new, no delete, and no copy of the caller's data anywhere. That is what lifetime-aware C++ looks like.