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.
