v.profile: Add JSON output format

[saket0187]

Fixes #6232

Problem Description

The v.profile module only supported plain text output with pipe-delimited or custom separators. We were required to add JSON support as well.

Solution

Implemented comprehensive output format support with three options:

1. Plain format (default): Traditional CSV-style output with quoted string values. Maintains full backward compatibility with existing scripts.

2. CSV format: Unquoted delimiter-separated values optimized for spreadsheet applications. Uses the same separator parameter as plain format but omits quotes for cleaner parsing.

3. JSON format: Structured output with proper data type handling. Each feature is represented as a JSON object containing:

   • category: Feature category number (always present, even without database)
   • distance: Distance along profile line
   • attributes

Implementation details:

• Uses GRASS GJSON API (G_json_* functions) for JSON serialization with proper NULL value handling
• Added comprehensive error checking with G_warning() for database operation failures
• Works correctly with and without database connections (Fi != NULL check)
• Updated format option to include "json" in descriptions

Testing

Automated Tests (test_v_profile.py):
Added testJsonFormat() that validates:

• JSON syntax correctness (parses without errors)
• Array structure with expected item count
• Required fields present (category, distance, attributes)
• Data type validation (category as int, distance as float)
• Value accuracy against expected results
• Attribute field completeness

All 6 test suite tests pass, including the new JSON format test.

Manual Testing with NC Basic dataset:

# Plain format (backward compatible)
v.profile input=poi_names_wake profile_map=roadsmajor buffer=200 profile_where="cat=354"

# CSV format
v.profile input=poi_names_wake profile_map=roadsmajor buffer=200 profile_where="cat=354" \
  format=csv separator=comma

# JSON format
v.profile input=poi_names_wake profile_map=roadsmajor buffer=200 profile_where="cat=354" \
  format=json

JSON Output example :-

[
    {
        "category": 572,
        "distance": 19537.972502200733,
        "attributes": {
            "cat": 572,
            "feature_id": "986138",
            "featurenam": "Greshams Lake",
            "class": "Reservoir",
            ...
        }
    }
]

[petrasovaa]

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