H7: Replace fully-qualified class names with imports and use var in HibernateCriteriaBuilder and CollectionBinder

## Summary

Two classes in `grails-data-hibernate7` were ported from H5 code and carry style issues that were intentionally deferred from PR #15568 to keep the review surface focused on the H7 integration work.

## Files

- `grails-data-hibernate7/core/src/main/groovy/grails/orm/HibernateCriteriaBuilder.java`
- Many fully-qualified class names used inline (e.g. `org.hibernate.Session`, `grails.gorm.DetachedCriteria`) instead of imports
- Local variable types that could use `var`

- `grails-data-hibernate7/core/src/main/groovy/org/grails/orm/hibernate/cfg/domainbinding/binder/CollectionBinder.java`
- Local variable declarations that could use `var` (e.g. line 95)

## Work

1. Replace inline FQCNs with import statements in `HibernateCriteriaBuilder.java`
2. Replace eligible local variable declarations with `var` in both files
3. Run `./gradlew :grails-data-hibernate7-core:test` to verify no regressions

## References

- PR #15568 (H7 Step 2) — review comments from @matrei

Start with grails-data-hibernate7/core/src/main/groovy/grails/orm/HibernateCriteriaBuilder.java and inspect its inline fully-qualified names and local variable declarations. Then review CollectionBinder.java, including the declaration around line 95. Replace eligible declarations as described and run ./gradlew :grails-data-hibernate7-core:test; done means both files use imports and var where appropriate with tests passing.

Written by the indexing model from the issue text.