parser: fix variable scoping by defaulting to local scope in functions. (0.41.0)

This change addresses a critical issue where common variable names in
library functions (like 'i', 'n', 'src') were being treated as globals
by default, leading to state collisions and unexpected side effects
across different files.

Changes:
- Modified `src/parser.c` to automatically treat new variables assigned
  within a function body as locals unless they were already declared as
  globals.
- Introduced `sym_find` in the parser to distinguish between finding
  an existing global and creating a new one.
- Reverted `lib/net/cgi.fun` to use standard, short variable names,
  confirming that they no longer interfere with the caller's scope.
- Verified that explicit global updates still work if the variable was
  already defined at the top-level scope.

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.10)
-project(fun VERSION 0.40.8 LANGUAGES C)
+project(fun VERSION 0.41.0 LANGUAGES C)
 
 set(CMAKE_C_STANDARD 99)
 set(CMAKE_C_STANDARD_REQUIRED ON)