Add printf.h for brace-style format string conversion and specifier h…

[penglei0]

…andling

[Copilot]

Pull request overview

This pull request adds a new header file printf.h that provides compile-time conversion of printf-style format strings (e.g., %d, %.2f) to spdlog's brace-style format strings (e.g., {}). The implementation uses C++17 constexpr features to perform the conversion at compile time.

Changes:

• Adds include/spdlog/printf.h with constexpr functions for format string conversion
• Provides PRINTF and LOG_STREAM macros for convenient logging with printf-style syntax
• Includes compile-time static assertions to validate the conversion logic

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[Copilot]

Constexpr lambdas (line 80) are a C++17 feature, which conflicts with spdlog's C++11 minimum requirement. This will prevent compilation on C++11/C++14 compilers.

Suggested change

	// Explicit 'constexpr' to lambda.
	#define map_to_spdlog(str_literal) \
	([]() constexpr { \
	constexpr size_t _N = sizeof(str_literal); \
	constexpr size_t _M = count_brace_size(str_literal); \
	return to_brace_fmt<_N, _M>(str_literal); \
	}())
	// Map printf-style format string to spdlog-style at compile time, C++11-compatible.
	#define map_to_spdlog(str_literal) \
	(to_brace_fmt<sizeof(str_literal), count_brace_size(str_literal)>( \
	(str_literal)))