[WIP] Fix redundancy of GetBackingStore method in Go client

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Original prompt

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This section details on the original issue you should resolve

<issue_title>GetBackingStore gets emitted for models interfaces when it shouldn't</issue_title> <issue_description>### What are you generating using Kiota, clients or plugins?

API Client/SDK

In what context or format are you using Kiota?

Nuget tool

Client library/SDK language

Go

Describe the bug

When generating a Go client with the backing store enabled, the GetBackingStore method gets emitted for the model interface when it is already defined in the BackedModel interface it already composes from.

This is redundant, making the compile time longer and leading to "heavier" binaries. (unless the Go compiler does some kind of smart trimming).

See this example in the Microsoft Graph SDK. https://github.com/microsoftgraph/msgraph-sdk-go/blob/2182e2493cff7e52e6f2273416f25f43c9fb2888/models/photo.go#L428

Expected behavior

The method should be trimmed from the interface definition like the methods from AdditionalDataHolder (GetAdditionalData, GetAdditionalData) and Parsable (Serialize, GetFieldDeserializers) are.

The solution should be implemented in the same way it is for those other methods.

How to reproduce

1. generate a go SDK with the backing store enabled
2. observe your model interfaces have the GetBackingStore method defined.

Open API description file

No response

Kiota Version

latest from main

Latest Kiota version known to work for scenario above?(Not required)

No response

Known Workarounds

No response

Configuration

No response

Debug output

Click to expand log

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</details>


### Other information

_No response_</issue_description>

<agent_instructions>use conventional commits.
add a changelog entry under unreleased, bugfix.</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
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• Fixes microsoft/kiota#7195

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