Code Quality: Variable shadowing and scope issues

[devin-ai-integration]

Static analysis revealed several code quality issues that should be addressed:

1. Variable Shadowing
Multiple instances of variable shadowing found in:

• n_helpers.c
• n_i2c.c
• n_serial.c

Example from n_helpers.c:

const char *err = _ChunkedReceive(...);
// Later in nested scope
const char *err = ERRSTR(...);  // Shadows outer err

2. Variable Scope Issues
Several variables have broader scope than necessary in:

• n_cjson_helpers.c
• n_cobs.c

Recommendations:

1. Rename shadowed variables to be more specific
2. Reduce variable scopes to minimum required
3. Consider using more descriptive variable names for error handling

Link to Devin run: https://app.devin.ai/sessions/845a7fbce65a49a6b7894d63572911f4