FIX: Runtime crash in textToJSON.add_response_to_json

[Aryama-srivastav]

Description

This PR fixes a runtime crash in textToJSON.add_response_to_json when the same field is processed more than once.

Previously, the first value for a field was stored as a scalar, but on repeated occurrences the code attempted to call .append(...) on that scalar, raising:
AttributeError: 'str' object has no attribute 'append'.

This change makes duplicate-field handling type-safe:

• if field appears once → keep scalar behavior
• if field appears again → convert stored scalar to list and append new value
• if already list → append normally

Fixes #182

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Test A (duplicate field path):

• • Ran:
    python -c "import sys; sys.path.insert(0,'src'); from backend import textToJSON; obj=textToJSON.new(textToJSON); obj._textToJSON__json={}; obj.add_response_to_json('Employee name','John'); obj.add_response_to_json('Employee name','Jane'); print(obj._textToJSON__json)"
• • Verified output:
    {'Employee name': ['John', 'Jane']}
    Verified no crash.

• Test B (single field behavior):

• • Ran:
    python -c "import sys; sys.path.insert(0,'src'); from backend import textToJSON; obj=textToJSON.new(textToJSON); obj._textToJSON__json={}; obj.add_response_to_json('Department','Operations'); print(obj._textToJSON__json)"
• • Verified output:
    {'Department': 'Operations'}

Test Configuration:

• Firmware version: N/A
• Hardware: Local development machine (Windows)
• SDK: N/A
• Python: 3.13
• Shell: PowerShell

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules