Add CppCoreGuidelines setup

[vladiant]

Summary

Hardens the warning configuration for the traincascade and test_traincascade targets by introducing a curated set of compiler diagnostics inspired by the C++ Core Guidelines and the cppbestpractices baseline. Flags are split per compiler (GNU, Clang, MSVC) so each toolchain enables the strictest set it actually supports.

Motivation

The previous configuration only enabled -Wall -Wextra -Wpedantic -Werror (or /W4 /WX). That misses a large class of bugs (shadowing, sign/integer conversions, switch coverage, format issues, uninitialized reads, aliasing violations, etc.) that the Core Guidelines explicitly call out. This PR raises the baseline without rewriting any production code.

Changes

• CMakeLists.txt
  • traincascade target: enable an extended warning set across MSVC / GCC / Clang. A few warnings that currently fire in legacy code (-Wold-style-cast, -Wsign-conversion, -Wconversion, MSVC /w14365) are commented out with a # Fix in code note so they can be re-enabled incrementally.
  • test_traincascade target: enables the full set including the warnings above, since the test code is clean.
• CMakeLists.txt: build fixes for vendored dependencies (zlib, macOS).
• GitHub Actions (ubuntu.yml, macos.yml, windows.yml, static_check.yml, codeql-analysis.yml): action version bumps, clang-tidy setup fix, disabled Java build, OpenCV version bump.

Per-compiler flag coverage

Common (GCC + Clang): -Wcast-qual -Wshadow -Wnull-dereference -Wmisleading-indentation -Wimplicit-fallthrough -Wswitch-enum -Wshift-negative-value -Wformat=2 -Wformat-security -fstrict-aliasing -Wstack-protector -fstack-protector-strong -Wnon-virtual-dtor -Woverloaded-virtual -Wuninitialized -Walloca -Wvla

GCC-only: -Wcast-align=strict -Warith-conversion -Wduplicated-branches -Wduplicated-cond -Wlogical-op -Wshift-overflow=2 -Wstrict-aliasing=3 -Wmaybe-uninitialized

Clang-only: -Wcast-align -Wlogical-op-parentheses -Wshift-overflow -Wconditional-uninitialized -Wsometimes-uninitialized

MSVC: /Zc:__cplusplus /Zc:preprocessor /Zc:inline plus the /w14xxx set covering shadowing, conversions, switch/enum, fallthrough, format, virtual/override hygiene, and uninitialized reads.

Validation

• CI updated and green on Ubuntu, macOS and Windows runners.
• clang-tidy job fixed and running in static_check.yml.

Follow-ups

Re-enable the warnings currently commented out as # Fix in code once the corresponding issues in traincascade are cleaned up:

• -Wold-style-cast
• -Wconversion / -Wsign-conversion (MSVC /w14365)