Fix cpplint findings: C-style casts, comma spacing, missing include.

Applies clang-format (project style) and converts C-style casts to
static_cast, as flagged by the cpplint check in CI. No behavior change:
rebuilt and re-ran the single-file smoke test, same histogram counts as
before. Also adds the <memory> include cpplint pointed out for
shared_ptr<>.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YbYBgosEJaDJTkCuqAtNHk

Author: matarzil