refactor(rust/signed-doc): Change collabs header to collaborators

[apskhem]

Description

!!BREAKING CHANGE!!

• Changed collabs header to collaborators
• Changed from the list of String to CatalystId

Related Issue(s)

Closes #387

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• My code follows the style guidelines of this project
• I have performed a self-review of my code
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• I have made corresponding changes to the documentation
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• I have added tests that prove my fix is effective or that my feature works
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[apskhem]

As I changed collaborators to use CatalystId instead of String, do we want it to be lazy or eager decoding? [do we want to parse cat-id at the moment we decode cbor (eager), or do we want to parse it when we first access thecollaborators part (lazy)] As this commit, I did eager decoding. But want opinion from others.

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 360/360}$ | ${\color{red}Fail: 0/360}$ |

[saibatizoku]

Looks good to me.