fix: Fix Go feature server entitykey serialization for version 3

[shuchu]

What this PR does / why we need it:

1, Update the Go version to 1.23. (Prepare for the OTEL implementation)
2, Fix the serialization EntityKey version 3 issue of Go Feature server. Now only version 3 serialization is supported.

Which issue(s) this PR fixes:

#5608

Misc

[shuchu]

cc: @jyejare Hi, the Github does not allow me to add you as a reviewer. But please help me to review it. This PR includes some of your code.

[Copilot]

Pull Request Overview

This PR updates the Go Feature Server to fix EntityKey serialization version 3 issues and upgrades Go to version 1.23. The changes focus on implementing proper serialization for EntityKey version 3 by adding a count prefix and reorganizing the serialization logic.

• Updated Go version from 1.22.0 to 1.23
• Fixed EntityKey serialization version 3 by adding join key count prefix and restructuring buffer layout
• Moved serializeValue function from redisonlinestore.go to onlinestore.go for better code organization

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
go.mod	Updates Go version to 1.23 and toolchain to 1.23.12
go/internal/feast/onlinestore/onlinestore.go	Implements EntityKey v3 serialization with key count prefix and moves serializeValue function
go/internal/feast/onlinestore/redisonlinestore.go	Removes serializeValue function (moved to onlinestore.go)
go/internal/feast/onlinestore/onlinestore_test.go	Adds unit test for serializeEntityKey function
go/internal/test/feature_repo/feature_store.yaml	Sets entity_key_serialization_version to 3
Makefile	Updates build dependencies and test targets

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