Fix clang-tidy errors

[aryanputta]

Summary

• replaces #pragma once with include guards in the public RSL headers flagged by clang-tidy
• switches Queue's simple mutex guards to std::scoped_lock
• parenthesizes the queue size assertion flagged by readability-math-missing-parentheses
• keeps the existing C++17 contract by locally suppressing the C++20-only modernize-use-constraints and modernize-use-std-numbers suggestions with comments

Fixes #168.

Validation

• pre-commit run --files include/rsl/algorithm.hpp include/rsl/monad.hpp include/rsl/no_discard.hpp include/rsl/overload.hpp include/rsl/parameter_validators.hpp include/rsl/queue.hpp include/rsl/random.hpp include/rsl/static_string.hpp include/rsl/static_vector.hpp include/rsl/strong_type.hpp include/rsl/try.hpp src/random.cpp tests/queue.cpp
• git diff --check
• c++ -std=c++17 -Iinclude -fsyntax-only -x c++-header include/rsl/queue.hpp
• c++ -std=c++17 -Iinclude -fsyntax-only -x c++-header include/rsl/algorithm.hpp
• c++ -std=c++17 -Iinclude -fsyntax-only -x c++-header include/rsl/no_discard.hpp

I could not run the full CMake/ROS test matrix locally on macOS: the repo preset assumes Linux lld, and a local CMake configure without that preset stops on missing ROS/Eigen dependencies. The GitHub Actions matrix should cover the full ROS/clang-tidy path.

[christophfroehlich]

Duplicate of #171

Can you please check the existing PR, and comment there