Compile .pyc files when unpacking wheels into distribution

Wheels don't carry .pyc files, but the Lambda distribution file probably should, to avoid incurring a startup time penalty. `chalice.deploy.packager.DependencyBuilder._install_wheels` should include a call to `compileall.compile_dir`.

Start in chalice.deploy.packager.DependencyBuilder._install_wheels and inspect how wheels are unpacked into the Lambda distribution. Add the requested compileall.compile_dir step, then verify that the resulting distribution contains compiled Python files and that the existing packaging behavior remains intact.

Written by the indexing model from the issue text.