[ruby] Introduce ApiModelBase to reduce code duplication

[Fryguy]

The Ruby code that is generated copies numerous methods into every model. This creates bloat both in file size and run-time memory usage. This commit introduces a base class for all models to store common methods. This commit's focus is only on static methods that do not change between models.

Part of #22051

@cliffano @zlx @autopp

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[Fryguy]

Some notable files to see the general diff pattern

• new api_model_base.rb: https://github.com/OpenAPITools/openapi-generator/pull/22052/files#diff-071a7c60f7deffda85dd3078cb31204e2e6b6db232e69ccf807af8fb89285eec
• petstore model animal.rb (previously no parent class): https://github.com/OpenAPITools/openapi-generator/pull/22052/files#diff-0ae5cb1a510282c3a229f4ae2f9a5a840965e68ee2ff8e9a7308a8ac45f21fff
• petstore model cat.rb (subclass of animal, which did not change): https://github.com/OpenAPITools/openapi-generator/pull/22052/files#diff-291e32f2fa0f5f299d029bda60b519005094ae1cfe7d9e07115a98b64e438923

[Fryguy]

I did want to point out I deleted those inline_object files in the ruby petstore sample because they aren't generated and look like something old and unused. If they aren't, let me know and I will restore them with manual changes matching the new pattern.

[wing328]

Is this PR ready for review?

[Fryguy]

Thanks for the poke @wing328 - I've un-drafted this PR.