Add performance and caching tests for stdout/stderr

[krassowski]

References

Code changes

Adds caching for results on the linkify method which is the most expensive step of rendering large errors and standard outputs.

User-facing changes

Faster stdout

Iterations	Before	After
1000	4s	3s
2000	18s	8s
3000	42s	22s
4000	1min 23s	41s

import sys

for i in range(4000):
    print(f"example.com {i} XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX www.", end='')
    sys.stdout.flush()

Faster stderr

Iterations	Before	After
1000	2s	1s
2000	7s	3s
3000	16s	7s
4000	30s	13s

import logging

logger = logging.getLogger()

for i in range(4000):
    logger.error(f"{i} XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX")

I had to increase --ServerApp.iopub_msg_rate_limit to 10000 as the stream was faster than jupyter-server was allowing for ("IOPub message rate exceeded").

Backwards-incompatible changes