dsh-lit-filecheck: Bringing lit + FileCheck test loop into DSH sessions

dsh-lit-filecheck is a DSH plugin maintained by Rcyc-1025, categorized as a workflow, providing three tools: lit_run, lit_rerun_failed, and filecheck. lit_run executes llvm-lit in the test suite root directory, reporting total counts and passed/failed/skipped results. It breaks down each block failure into a single CHECK diagnostic, identifying the CHECK line in the test file and the error line in the actual IR. lit_rerun_failed only reruns tests that failed in the previous run of this plugin instance, without performing a full scan. filecheck runs FileCheck separately on a pair of a test file containing CHECK lines and an actual IR file, reporting mismatches. The plugin is an ESM module that does not start background tasks or persist state. The article covers configuration options, usage of the three tools, CHECK diagnostic parsing, logs and error codes, test verification status, and known limitations, including a Table of Contents and a GitHub link.