Remove limitations on nested relations in CompositeIDs

[gwynne]

This update enables embedding @Composite[Optional]Parent properties in a @CompositeID, as well as:

• Removes some more fatalError()s and uses of force-unwrapping from Fluent
• Improves suggestions in fatal errors from Parent/OptionalParent/Siblings
• More reliable behavior of QueryBuilder.count() when the queried model has a composite ID
• Minor performance improvements in Collection<Model>.delete(force:on:)

[codecov-commenter]

Codecov Report

Merging #553 (4605b10) into main (b821ac3) will decrease coverage by 0.21%. The diff coverage is 80.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #553 +/- ## ========================================== - Coverage 47.33% 47.12% -0.21% ========================================== Files 106 106 Lines 6180 6154 -26 ========================================== - Hits 2925 2900 -25 + Misses 3255 3254 -1 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `47.12% <80.00%> (-0.21%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | Coverage Δ | | |---|---|---| | [Sources/FluentKit/Properties/Children.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9DaGlsZHJlbi5zd2lmdA==) | `41.91% <ø> (-0.95%)` | :arrow_down: | | [Sources/FluentKit/Properties/CompositeID.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9Db21wb3NpdGVJRC5zd2lmdA==) | `88.23% <ø> (+10.18%)` | :arrow_up: | | [Sources/FluentKit/Properties/OptionalChild.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9PcHRpb25hbENoaWxkLnN3aWZ0) | `24.39% <ø> (-1.60%)` | :arrow_down: | | [Sources/FluentKit/Properties/OptionalParent.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9PcHRpb25hbFBhcmVudC5zd2lmdA==) | `33.33% <50.00%> (ø)` | | | [Sources/FluentKit/Properties/Parent.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9QYXJlbnQuc3dpZnQ=) | `44.44% <50.00%> (-2.23%)` | :arrow_down: | | [Sources/FluentKit/Properties/Siblings.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9TaWJsaW5ncy5zd2lmdA==) | `49.76% <50.00%> (-0.48%)` | :arrow_down: | | [.../FluentKit/Query/Builder/QueryBuilder+Filter.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUXVlcnkvQnVpbGRlci9RdWVyeUJ1aWxkZXIrRmlsdGVyLnN3aWZ0) | `43.54% <50.00%> (-5.03%)` | :arrow_down: | | [...uentKit/Query/Builder/QueryBuilder+Aggregate.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUXVlcnkvQnVpbGRlci9RdWVyeUJ1aWxkZXIrQWdncmVnYXRlLnN3aWZ0) | `41.17% <87.50%> (+0.58%)` | :arrow_up: | | [Sources/FluentKit/Database/DatabaseInput.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvRGF0YWJhc2UvRGF0YWJhc2VJbnB1dC5zd2lmdA==) | `91.42% <100.00%> (+0.25%)` | :arrow_up: | | [Sources/FluentKit/Operators/ValueOperators.swift](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvT3BlcmF0b3JzL1ZhbHVlT3BlcmF0b3JzLnN3aWZ0) | `68.83% <100.00%> (-1.17%)` | :arrow_down: | | ... and [3 more](https://codecov.io/gh/vapor/fluent-kit/pull/553?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | |

[VaporBot]

These changes are now available in 1.39.1