Incorrect handling of public:cached keys in AtKey.fromString()

[srieteja]

Describe the bug

AtKey.fromString() is expecting all cached keys to be in the form of 'cached:@sharedWith:key@sharedBy', which works perfectly fine for shared keys. But incase the key is cached:public, the method is still behaving/responding as if the key is cached shared key.

Steps to reproduce

1. First I manually constructed a public cached key say 'cached:public:test_key@bob'
2. Then I pass the previously constructed atKey to AtKey.fromString()
3. And then an exception is thrown Exception: Exception: atSign public does not start with an "@"
4. My inference is that the method is assuming 'public' is the sharedWith atsign. And this is an issue because cached:public does not have a sharedWith atsign also public should not be read as an atsign.

Expected behavior

Expected behaviour from AtKey.fromString() for a key 'cached:public:test_key@bob' should be as follows:

• public keyword in the key should indicate that it is a shared key
• 'test_key' should be considered as the key
• '@bob' should be considered the sharedBy atsign
• sharedWith of this key should be null

Screenshots

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Were you using an atApplication when the bug was found?

No response

Additional context

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