feat(lex_parser): 提取字符判断函数并增强解析器断言

将 `is_next_line` 内联函数重命名为 `lex_parse_is_endline` 并新增 `lex_parse_is_whitespace` 函数，统一用于词法解析中的字符分类。同时加强多个解析函数的输入参数断言，提升代码健壮性。

此外，修正了 `lex_parse_skip_whitespace` 中的逻辑错误，并优化部分注释和控制流结构。

feat(pprocessor): 初始化预处理器模块并添加基础功能实现

新增预处理器模块 `pprocessor`，包括宏定义、条件编译状态管理以及基本的指令解析框架。实现了标识符解析、空白跳过、关键字查找等功能，并初步支持 `#define` 指令的对象类宏替换。

该提交还引入了一组测试用例，覆盖多种宏展开场景及边界情况，确保预处理器的核心行为符合预期。

libs/pprocessor/tests/pp/README

@@ -0,0 +1,96 @@
+Tiny C Compiler - C Scripting Everywhere - The Smallest ANSI C compiler
+-----------------------------------------------------------------------
+
+Features:
+--------
+
+- SMALL! You can compile and execute C code everywhere, for example on
+  rescue disks.
+
+- FAST! tcc generates optimized x86 code. No byte code
+  overhead. Compile, assemble and link about 7 times faster than 'gcc
+  -O0'.
+
+- UNLIMITED! Any C dynamic library can be used directly. TCC is
+  heading toward full ISOC99 compliance. TCC can of course compile
+  itself.
+
+- SAFE! tcc includes an optional memory and bound checker. Bound
+  checked code can be mixed freely with standard code.
+
+- Compile and execute C source directly. No linking or assembly
+  necessary. Full C preprocessor included.
+
+- C script supported : just add '#!/usr/local/bin/tcc -run' at the first
+  line of your C source, and execute it directly from the command
+  line.
+
+Documentation:
+-------------
+
+1) Installation on a i386/x86_64/arm/aarch64/riscv64
+   Linux/macOS/FreeBSD/NetBSD/OpenBSD hosts.
+
+   ./configure
+   make
+   make test
+   make install
+
+   Notes: For FreeBSD, NetBSD and OpenBSD, gmake should be used instead of make.
+   For Windows read tcc-win32.txt.
+
+makeinfo must be installed to compile the doc.  By default, tcc is
+installed in /usr/local/bin.  ./configure --help  shows configuration
+options.
+
+
+2) Introduction
+
+We assume here that you know ANSI C. Look at the example ex1.c to know
+what the programs look like.
+
+The include file <tcclib.h> can be used if you want a small basic libc
+include support (especially useful for floppy disks). Of course, you
+can also use standard headers, although they are slower to compile.
+
+You can begin your C script with '#!/usr/local/bin/tcc -run' on the first
+line and set its execute bits (chmod a+x your_script). Then, you can
+launch the C code as a shell or perl script :-) The command line
+arguments are put in 'argc' and 'argv' of the main functions, as in
+ANSI C.
+
+3) Examples
+
+ex1.c: simplest example (hello world). Can also be launched directly
+as a script: './ex1.c'.
+
+ex2.c: more complicated example: find a number with the four
+operations given a list of numbers (benchmark).
+
+ex3.c: compute fibonacci numbers (benchmark).
+
+ex4.c: more complicated: X11 program. Very complicated test in fact
+because standard headers are being used ! As for ex1.c, can also be launched
+directly as a script: './ex4.c'.
+
+ex5.c: 'hello world' with standard glibc headers.
+
+tcc.c: TCC can of course compile itself. Used to check the code
+generator.
+
+tcctest.c: auto test for TCC which tests many subtle possible bugs. Used
+when doing 'make test'.
+
+4) Full Documentation
+
+Please read tcc-doc.html to have all the features of TCC.
+
+Additional information is available for the Windows port in tcc-win32.txt.
+
+License:
+-------
+
+TCC is distributed under the GNU Lesser General Public License (see
+COPYING file).
+
+Fabrice Bellard.