fix(clippy): Fix new lints in nightly clippy

[teor2345]

Motivation

We regularly fix new clippy lints to make new Rust releases easier to upgrade to, and to make Zebra easier to maintain.

Solution

• derive Default in more places
• implement PartialEq manually when Hash is implemented manually
• document some functions to resolve missing docs warnings in Docker builds

Review

Anyone can review this PR, it is a low priority.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
  • Does it change concurrent code, unsafe code, or consensus rules?
• How do you know it works? Does it have tests?

[codecov]

Codecov Report

Merging #5959 (e5985ea) into main (99a2da6) will increase coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head e5985ea differs from pull request most recent head 577cd7b. Consider uploading reports for the commit 577cd7b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5959      +/-   ##
==========================================
+ Coverage   78.06%   78.11%   +0.04%     
==========================================
  Files         311      311              
  Lines       38919    38914       -5     
==========================================
+ Hits        30384    30398      +14     
+ Misses       8535     8516      -19     

[arya2]

Thank you for the proactive fixes!