feat: chaining the extraction of multiple properties of the same subject

[haraldmaida]

For asserting custom structs it should be possible to chain the extraction of multiple properties from the same subject for individual assertions.

For example:

use asserting::prelude::*;

struct Person {
    name: String,
   age: u8,
}

let person = Person {
    name: "Silvia".into(),
    age: 25
};

assert_that!(person)
    .extracting_ref("name", |p| &p.name)
    .is_equal_to("Silvia")
    .and()
    .extracting_ref("age", |p| &p.age)
    .is_at_least(18);

As this requires, ,that the type of the extracted property implements ToOwned (or Clone), the new method extracting_ref is added (instead of re-purposing the existing method extracting).

[codecov]

Codecov Report

❌ Patch coverage is 56.80346% with 400 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.95%. Comparing base (18675f5) to head (e77929e).
⚠️ Report is 28 commits behind head on main.

Files with missing lines	Patch %	Lines
src/derived_spec/mod.rs	50.12%	387 Missing and 4 partials ⚠️
src/iterator/mod.rs	87.14%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #88      +/-   ##
==========================================
- Coverage   92.85%   87.95%   -4.91%     
==========================================
  Files          41       42       +1     
  Lines        5756     6649     +893     
  Branches     5756     6649     +893     
==========================================
+ Hits         5345     5848     +503     
- Misses        345      731     +386     
- Partials       66       70       +4     

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