feat: deduplicate bucket names when ingesting from file

[lavafroth]

Fixes #156

Changes

• Adds a string hashset (empty struct map) to keep track of bucket names that are already seen
• Continues the file scanning loop if a bucket name is seen
• Sends the bucket to the channel and adds it to the set of seen bucket names otherwise

[sa7mon]

Good work! Can you add a unit test for this method to verify duplicate buckets don't get scanned? Finding a way to do it without adding test files would be ideal, but if the only clean way is to add a test_buckets.txt file to the module then so be it.

[lavafroth]

I'll create a helper function that does this using an io.Reader so that we can test that with a strings.NewReader for a test string.

[sa7mon]

Last thing: README.md should be updated as well. Under the -bucket-file section after the example file code block add:

Bucket names listed multiple times will only be scanned once.

[sa7mon]

Thanks for the contribution!