TRCLI-162: Multisuite parser to process multiple suites in a single test plan

[acuanico-tr-galt]

Issue being resolved: #348

Solution description

If the test automation spans multiple TestRail suites, the multisuite parser (--special-parser multisuite) allows you to create a single test plan with one run per suite from a single JUnit XML report. The CLI automatically detects which suite each test case belongs to, groups them accordingly, and creates or updates a test plan with the appropriate structure.

• All test cases must have case IDs (C123 format in test names or test_id properties)
• Must use --case-matcher name or --case-matcher property (not auto)
• All cases must belong to the same project (cross-project cases are skipped with warnings)

Changes

• multisuite_uploader.py to properly fetch cases, project validation with cross project filtering.

Potential impacts

None. Changes are all backwards compatible.

Steps to test

Happy path to test implemented scenario

PR Tasks

• PR reference added to issue
• README updated
• Unit tests added/updated