[RF] Fix implementation of HS3 importers

[maxgalli]

Fix by @guitargeek.
The RooWSFactoryTool expression handler was not correctly matching branckets, leading to failures when importing valid JSON filed with RooProdPdf objects.

Can be tested with the following reproducer:
python3 dump_json_to_workspace.py datacard_part1_nosys.json

where dump_json_to_workspace.py is

import ROOT
import sys
import os

# Check if the user provided an input file
if len(sys.argv) != 2:
    print("Usage: python script.py <input_json_file>")
    sys.exit(1)

# Get the input file from command line
input_file = sys.argv[1]

# Ensure the file exists
if not os.path.isfile(input_file):
    print(f"Error: File '{input_file}' not found.")
    sys.exit(1)

# Extract the base name without extension
base_name = os.path.splitext(os.path.basename(input_file))[0]
output_file = f"{base_name}_imported.root"

ws = ROOT.RooWorkspace("w")
tool = ROOT.RooJSONFactoryWSTool(ws)
tool.importJSON(input_file)
ws.writeToFile(output_file)

and datacard_part1_nosys.json is

{"distributions":[{"factors":[],"name":"nuisancePdf","type":"product_dist"}],"metadata":{"hs3_version":"0.2","packages":[{"name":"ROOT","version":"6.30.07"}]}}

[github-actions]

Test Results

    16 files      16 suites   5d 8h 33m 43s ⏱️
 2 735 tests  2 732 ✅ 0 💤 3 ❌
42 372 runs  42 369 ✅ 0 💤 3 ❌

For more details on these failures, see this check.

Results for commit 4cc6030.

[guitargeek]

Thank you very much!