Remove pointer "as" casts

[jnbooth]

Instead of using as * pointer conversions, it's recommended to use pointer::cast and pointer::cast_mut. This approach is safer because pointer::cast won't accidentally cast from immutable to mutable or vice versa (see #1402), and pointer::cast_mut only casts between mutable and immutable, so it won't accidentally cast to the wrong type (see #1401). This PR refactors the remaining pointer conversions that were not addressed by #1401 or #1402. Once all three are merged, the ptr_as_ptr and ptr_cast_constness lints can be enabled. Alternatively, #1401 and #1402 can be merged, and then those lints can be added to this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (55106f0) to head (e5f02ce).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1403   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           75        75           
  Lines        13124     13124           
=========================================
  Hits         13124     13124           

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[BenFordTytherington]

Looks like a good refactor to me, makes the code a little easier to read