[RDF] Support bar charts in RDataFrame for Alphanumeric Bins

[Aditya-138-12]

This Pull request:

Add new RBarChart class and MakeBarChartTH1D method to RDataFrame to support visualization of categorical string data as bar charts.

Changes or fixes:

• Automatically handles bin labeling
• Supports string-based categories
• Returns manipulable TH1D histogram

Example Usage

In ROOT CLI

auto df = ROOT::RDataFrame(10);
auto df2 = df.Define("Category", []() { 
    std::vector<std::string> categories = {"A", "B", "C", "A", "B"}; 
    return categories[rand() % 5]; 
});

auto barChart = df2.MakeBarChartTH1D("Category", "test_chart", "Test Categories");

barChart.GetHistogram()->Draw("HIST");

Checklist:

• [✅] tested changes locally
• [✅] updated the docs (if necessary)

This PR fixes #17057

[Aditya-138-12]

Hi @vepadulano, I have messed up with this PR due to some merges, I will open up a new one.
Thank you for your support!!