Fix clippy lints

[olivereanderson]

Description of change

Fixes new warnings from clippy +nightly.

The error variant identity_iota_core::Error::DIDUpdateError wrapped a tuple consisting of a static string and an optional iota_client::Error. The size of the aforementioned tuple is then 16 + 120 = 136 bytes thus exceeding clippy's large_error_threshould which is 128 bytes by default (see clippy::result_large_err). I reduced the size of this variant by boxing the wrapped iota_client::Error which is why this is marked as a breaking change.

Links to any relevant issues

unblocks #1067.

Type of change

Add an x to the boxes that are relevant to your changes.

• Bug fix (a non-breaking change which fixes an issue)
• Enhancement (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Fix

How the change has been tested

Runs under cargo test --all-features.

Change checklist

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• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes