Fix: CIDR Calculator (/tools/cidr-calculator.php) — fixed three bugs in Range → CIDR mode that…

CIDR Calculator (/tools/cidr-calculator.php) — fixed three bugs in Range → CIDR mode that produced wrong results (and could hang the page) for any range with the high bit set, i.e. any IP ≥ 128.0.0.0. Signed-vs-unsigned 32-bit arithmetic was breaking the aligned-block search, the shrink loop, and the next-start advance. Verified with a 100-assertion offline test suite covering all three modes, /0 – /32 prefixes, classful boundaries, RFC 3021 /31 handling, private/loopback detection, and range coverage round-trips.