Replace std::regex_replace when stripping leading/trailing space

[aldehir]

Fixes #16

Looks like std::regex_replace() does not respect anchors, at least not in Windows.

Minimal reproducing example (Microsoft (R) C/C++ Optimizing Compiler Version 19.44.35221 for x64)

#include <iostream>
#include <regex>

int main() {
    auto text = "\nthis contains\n\nmultiple\nline\n\nbreaks\n\n";

    std::cout << "== Leading ==\n";
    auto bad = std::regex_replace(text, std::regex(R"(^\s)"), "");
    std::cout << "Bad: " << bad << "\n";
    std::cout << "==\n";

    std::string good = text;
    good.erase(0, good.find_first_not_of(" \t\r\n"));
    std::cout << "Good: " << good << "\n";
    std::cout << "==\n";

    std::cout << "== Trailing ==\n";
    bad = std::regex_replace(text, std::regex(R"(\s$)"), "");
    std::cout << "Bad: " << bad << "\n";
    std::cout << "==\n";

    good = text;
    auto pos = good.find_last_not_of(" \t\n\r\f\v");
    good.resize(pos == std::string::npos ? 0 : pos + 1);
    std::cout << "Good: " << good << "\n";
    std::cout << "==\n";
}

== Leading ==
Bad: this contains
multiple
line
breaks

==
Good: this contains

multiple
line

breaks


==
== Trailing ==
Bad: 
this contains
multiple
line
breaks
==
Good: 
this contains

multiple
line

breaks
==

Passes all the tests, excluding the gated templates I don't have.

$ ctest -R test-supported-template -j 24
...
100% tests passed, 0 tests failed out of 220

Total Test time (real) =  32.38 sec

The following tests did not run:
         11 - test-supported-template-google-gemma-7b-it (Skipped)
         12 - test-supported-template-CohereForAI-c4ai-command-r-plus (Skipped)
         14 - test-supported-template-meta-llama-Llama-3.2-3B-Instruct (Skipped)
         15 - test-supported-template-meta-llama-Llama-3.1-8B-Instruct (Skipped)
         16 - test-supported-template-meta-llama-Meta-Llama-3-8B-Instruct (Skipped)
         18 - test-supported-template-meta-llama-Llama-2-7b-chat-hf (Skipped)
         54 - test-supported-template-CohereForAI-aya-expanse-8b (Skipped)
         55 - test-supported-template-databricks-dbrx-instruct (Skipped)

[ochafik]

Thanks @aldehir !!