improved adhoc string scanning

[domanchi]

Summary

Adhoc string scanning is hella useful. e.g.

$ detect-secrets scan --string 'butactuallynotasecret'
...
Base64HighEntropyString: False

However, sometimes (especially for the HighEntropyString plugins), we want to see why it failed. This is existing behavior in 0.14.3; this PR carries this functionality forward. With this change, it will be:

$ detect-secrets scan --string 'butactuallynotasecret'
...
Base64HighEntropyString: False (3.404)

Reviewer Notes

It was somewhat difficult to surface the non-secret to the scan layer in a generic manner (i.e. without using if plugin in {Base64HighEntropyString}), so I had to be creative with the analyze_line and analyze_string functionality. As a result, for people using the analyze_string function directly (like the test case), they would need to be responsible for filtering out the secret themselves.

Not ideal, but it's the best way I could find.

This PR also introduces another gotcha -- for our DI system, we now leverage the pythonic fashion of duck-typing to determine whether there are enough required parameters to inject into the function. This needed to be done to support cases where the underlying function had default values for their parameters (e.g. HighEntropyStringsPlugin.analyze_line), and as such, we don't need to supply all the parameters that a function needs. However, this also means that if the underlying function raises an uncaught TypeError, it will be silenced by the DI system.

I guess future improvements could be done to distinguish default parameters from non-default parameters in a function declaration, but I didn't want to dive too deep into Python magic internals for this PR.

[calvinli]

looks fine overall, just have a few comments

[calvinli]

lgtm