Fix #4082: Remove name() method generation for unnamed Smithy enums

[drganjoo]

This PR addresses issue #4082 by removing the generation of the name() method for unnamed Smithy enums in Python code output.

Changes

• Modified the enum code generator to check if an enum is unnamed (string enum)
• Skip generating the name() method for unnamed enums, as they don't have separate name identifiers
• Retained the name() method generation for properly named enums

Testing

Verified that code generation for unnamed enums no longer includes the problematic name() method that was previously trying to reference undefined null values.

Closes: $4082

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

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