Allocationless parsing

[rsore]

A major goal of this library is to minimize the amount of heap allocations that are done during parsing. Previously, all arguments passed to the parse method of the Parser were inserted into a std::vector. One by one, the front element would be popped off and processed. Though this solution was simple, it was expensive due to two main reasons. First, we allocated a vector to store the elements, which wasn't necessary since we already received the elements in a container—a raw C-string array. Second, erasing elements from the front multiple times is costly, as it requires moving the remaining elements one by one every time.

In this development branch, I have removed the usage of std::vector and replaced it with a view. I use the std::views::counted function, which, when used with a raw array of C-strings, returns a std::span. This change allows us to apply modern container access practices with the plain old array. Instead of removing elements from the original array, I can now shrink the view in each iteration until the view is empty.

The main difference in this branch can be seen by comparing simplified versions of the two implementations.
The old version is as follows:

std::vector<std::string_view> args(argc);
for (int i{}; i < argc; ++i)
{
    arguments[i] = argv[i];
}
while (!args.empty())
{
    // Do some work...
    args.erase(args.begin());
}

In contrast, the new version is:

auto args = std::views::counted(argv, argc);
while (!args.empty())
{
    // Do some work...
    args = std::views::drop(args, 1);
}

Before deciding on this approach, I experimented with a custom container that used std::span internally. While it initially seemed to work, it became unnecessarily complex for my needs. I retained some utility functions I had already written for testing, as they will likely be useful in the future.

This optimization should lead to significant performance improvements, particularly in scenarios involving a large number of arguments.

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"