refactor(eslint-plugin-nestjs-tools): extend return class instance checks

[getlarge]

... and improve readability

Description

Handle more service's methods return types.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Refactor (a code change that neither fixes a bug nor adds a feature)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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✅ Successfully ran 1 target

• nx affected -t lint,test,build --parallel=2

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[sonarcloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
80.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud