perf(NODE-5986): parallelize SRV/TXT resolution

[addaleax]

Just a small thing I noticed while looking at the driver code, this is a quick win to improve connection establishment performance.

Description

What is changing?

Is there new documentation needed for these changes?

What is the motivation for this change?

Release Highlight

Query SRV and TXT records in parallel

When connecting using a convenient SRV connection string (mongodb+srv://) hostnames are obtained from an SRV dns lookup and some configuration options are obtained from a TXT dns query. Those DNS operations are now performed in parallel to reduce first-time connection latency.

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[durran]

Just verifying from spec: "TXT records MAY be queried either before, in parallel, or after SRV records."