[common] remove uneeded allocations in logs (#3409)

+ make filename be a const char
also mark as `noexcept` to avoid emission of uneeded unwind paths :)

Signed-off-by: lizzie <lizzie@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3409
Reviewed-by: DraVee <dravee@eden-emu.dev>
Reviewed-by: Maufeat <sahyno1996@gmail.com>
Reviewed-by: crueter <crueter@eden-emu.dev>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

src/common/logging/log_entry.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -9,17 +12,15 @@
 
 namespace Common::Log {
 
-/**
- * A log entry. Log entries are store in a structured format to permit more varied output
- * formatting on different frontends, as well as facilitating filtering and aggregation.
- */
+/// @brief A log entry. Log entries are store in a structured format to permit more varied output
+/// formatting on different frontends, as well as facilitating filtering and aggregation.
 struct Entry {
     std::chrono::microseconds timestamp;
     Class log_class{};
     Level log_level{};
     const char* filename = nullptr;
     unsigned int line_num = 0;
-    std::string function;
+    const char* function = nullptr;
     std::string message;
 };