[enhancement] Add `worst_case_throughput` minimization results to benchmark reports

[rw1nkler]

What's hard to do? (limit 100 words)

worst_case_throughput minimization does not report the actual throughput it achieved in a visible way.
This makes it hard to evaluate performance, especially in multi_proc codegen.
Without this information, it is difficult to understand the real performance of the design.

Current best alternative workaround (limit 100 words)

Generate each proc separately with strict constraints on worst_case_throughput.
This ensures the required throughput is met, but adds extra steps and complexity to the workflow.

Additionally, one can increase verbosity of the logs and read it on stdout:

xls/xls/scheduling/run_pipeline_schedule.cc

Line 567 in 65aa30d

LOG(INFO) << "Minimized worst-case throughput for proc '" << f->name()

Your view of the "best case XLS enhancement" (limit 100 words)

Extend the opt_ir_benchmark report to include the achieved worst_case_throughput from the minimization pass.
Showing this value next to the pipeline scheduling data would make it much easier to assess whether performance goals were met.