r.stats: add JSON output

[kritibirda]

Using parson, add JSON output support to r.stats module.

For cell stats, the output looks like:

[
    {
        "labels": [
            {
                "value": 1,
                "label": "CARY",
                "name": "towns"
            },
            {
                "value": 55,
                "label": "",
                "name": "urban"
            }
        ],
        "area": 23475900,
        "count": 234759,
        "percent": 11.651235678463038
    },
    {
        "labels": [
            {
                "value": 2,
                "label": "GARNER",
                "name": "towns"
            },
            {
                "value": 55,
                "label": "",
                "name": "urban"
            }
        ],
        "area": 14142700,
        "count": 141427,
        "percent": 7.0191102718021128
    },
    {
        "labels": [
            {
                "value": 3,
                "label": "APEX",
                "name": "towns"
            },
            {
                "value": 55,
                "label": "",
                "name": "urban"
            }
        ],
        "area": 1519700,
        "count": 15197,
        "percent": 0.75423659414805311
    }
]

For raw stats, the output looks like:

[
    {
        "easting": 639315,
        "northing": 228495,
        "col": 932,
        "row": 1,
        "labels": [
            {
                "value": 6,
                "label": "RALEIGH-WEST",
                "name": "towns"
            },
            {
                "value": 55,
                "label": "",
                "name": "urban"
            }
        ]
    },
    {
        "easting": 639325,
        "northing": 228495,
        "col": 933,
        "row": 1,
        "labels": [
            {
                "value": 6,
                "label": "RALEIGH-WEST",
                "name": "towns"
            },
            {
                "value": 55,
                "label": "",
                "name": "urban"
            }
        ]
    }
]

The labels array has the numerical value, categorical name, and the name of the inputs associated with the stat. I am unsure if these fields can be named better.

Once the JSON format is decided, I will add tests and update the documentation as well.

[cwhite911]

@kritibirda26 let's pick up on r.report first ( PR: https://github.com/OSGeo/grass/pull/3033) before starting on r.stats. It should be simpler and will help figure out how to address r.stats.

[kritibirda]

Makes sense @cwhite911

[kritibirda]

I have added a comment on the r.report PR to discuss the schema further.

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[echoix]

The codecov shouldn't be sending comments, it was explicitly disabled in config. Is it because the branch doesn't include the config file (not enough updated from main)?

[echoix]

Seems like it was the case..

[kritibirda]

@cwhite911 The PR is ready for review.

[echoix]

Before merging, can you make sure that your PRs are either formatted according to clang format 18 (changed 2 days ago), or merged from main?

[echoix]

Solved conflicts. Also renamed the test folder so it can be collected by gunittest