feat: add utf8 format

- move utf8 stream and format patch from string to patch namespace.
- add ordinay format alias and utf8 format in our format patch.
- add char8_t and char inter-cast in string reinterpret namespace.
- fix bug of utf8 formatter.
- add test for utf8 format.

testbench/yycc/patch/format.cpp

@@ -0,0 +1,35 @@
+#include <gtest/gtest.h>
+#include <yycc.hpp>
+#include <yycc/patch/format.hpp>
+
+#define FORMAT ::yycc::patch::format
+
+namespace yycctest::patch::format {
+
+    static constexpr char8_t PROBE[] = u8"hello";
+    static std::u8string PROBE_STRING(PROBE);
+    static constexpr std::u8string_view PROBE_STRING_VIEW(PROBE);
+
+    TEST(PatchFormat, OrdinaryFormat) {
+        auto rv = FORMAT::format("{}{}{}{}{}{} world!",
+                                 PROBE[0],
+                                 PROBE_STRING.data(),
+                                 PROBE_STRING.c_str(),
+                                 PROBE,
+                                 PROBE_STRING,
+                                 PROBE_STRING_VIEW);
+        EXPECT_EQ(rv, "104hellohellohellohellohello world!");
+    }
+
+    TEST(PatchFormat, Utf8Format) {
+        auto rv = FORMAT::format(u8"{}{}{}{}{}{} world!",
+                                 PROBE[0],
+                                 PROBE_STRING.data(),
+                                 PROBE_STRING.c_str(),
+                                 PROBE,
+                                 PROBE_STRING,
+                                 PROBE_STRING_VIEW);
+        EXPECT_EQ(rv, u8"104hellohellohellohellohello world!");
+    }
+
+}

testbench/yycc/patch/stream.cpp

@@ -0,0 +1,31 @@
+#include <gtest/gtest.h>
+#include <yycc.hpp>
+#include <yycc/patch/stream.hpp>
+#include <yycc/string/reinterpret.hpp>
+#include <sstream>
+
+#define REINTERPRET ::yycc::string::reinterpret
+using namespace std::literals::string_view_literals;
+using namespace ::yycc::patch::stream;
+
+namespace yycctest::patch::stream {
+    
+    TEST(PatchStream, StringView) {
+        std::stringstream ss;
+        ss << u8"hello"sv;
+        EXPECT_EQ(REINTERPRET::as_utf8_view(ss.view()), u8"hello"sv);
+    }
+
+    TEST(PatchStream, CStrPtr) {
+        std::stringstream ss;
+        ss << u8"hello";
+        EXPECT_EQ(REINTERPRET::as_utf8_view(ss.view()), u8"hello");
+    }
+
+    TEST(PatchStream, Character) {
+        std::stringstream ss;
+        ss << u8'y';
+        EXPECT_EQ(REINTERPRET::as_utf8_view(ss.view()), u8"y");
+    }
+
+}