ci: kTLS specific nix devShell

[dougch]

Resolved issues:

n/a

Description of changes:

We're running our kTLS tests under qemu without acceleration, which take over an hour. This change creates a minimal nix devShell with no python, corretto, aws-lc, etc.

High level timing currently:

1. nix devshell - 15 min
2. build - 30 min
3. test - 15 min

(current PR) Running all unit tests with this minimal devShell takes 49 minutes. This effectively eliminates the devshell timing from above.

Call-outs:

Other options:

• CodeBuilds recent announcement is likely a better long term fix, we'll merge this as-is.
• Running only unit ktls drops the runtime to 38 minutes.
• rm a bunch of unit tests; build time is the long pole, so the fewer tests we build, the faster it is.
• run a full test run on a schedule and just do the minimum for the PR workflow.

Testing:

How is this change tested (unit tests, fuzz tests, etc.)? locally; Codebuild

Is this a refactor change? If so, how have you proved that the intended behavior hasn't changed?

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[dougch]

drafting this; the new CodeBuild Ec2 instance runner is way faster.