Method to modify test input

[wileyj]

ref: https://github.com/stacks-network/stacks-core/pull/5978

idea is to provide a method to alter test functionality like :

assert!(last_block.tx_events.len() > 2000);

since running in CI is flaky with a higher value.

a few ideas:

• using an env var to set the value lower when running on smaller harder
• function to detect what type of hardware the code is running on
• nextest.toml may be useful here as well to provide a profile to enable/disable this switch