260 Parallelize multiple source fetch requests

[schuylermartin45]

We now use futures to download multiple source files concurrently.

Also introduces a --dry-run mode that dumps the recipe file to STDOUT instead of overwriting the recipe file.

Putting this PR up as a Draft until I can figure out why some of the bump_recipe_cli tests are significantly slower after this change (causing the tests to take 4 seconds to 35 seconds). That issue is now tracked in #265 as it appears to have no known user impact and is tied to the test environment.

[schuylermartin45]

The test_bump_recipe_cli() tests that reference

• gsm-amzn2-aarch64_version_bump.yaml
• libprotobuf_version_bump.yaml

cause the slow down. Each of these cases takes ~30 seconds to complete. They both have multiple sources but they are fully mocked.

[schuylermartin45]

The slow down goes away if I remove pyfakefs as a test fixture for test_bump_recipe_cli()

[schuylermartin45]

Upgrading to pyfakefs to 5.7.2 seems to help, but it could be transient. Some runs take 4 seconds, other runs still take 30+ seconds.

[schuylermartin45]

Reverted back to the older version, definitely transient. I just didn't run enough instances to see a shorter runtime.

[schuylermartin45]

Can't reproduce this slow down in a real (non-test) environment. Will spin-off this issue to another ticket, as it does not affect users.