Add a set of microbenchmarks to the test suite

To make it easier to detect and analyze performance regressions.

- [x] msgpipeline
- [x] storage/sql
- [ ] target/queue
- [ ] target/remote
- [ ] endpoint/smtp

Start by locating the existing microbenchmarks for msgpipeline and storage/sql in the Go test suite, then follow their structure for the unchecked target/queue, target/remote, and endpoint/smtp areas. Done means those three components have comparable benchmarks that make performance regressions easier to detect and analyze.

Written by the indexing model from the issue text.