Move serialization back out of SplitShardCountSummary

[bcully]

Serialization of this field is determined by the serialization of the request in which it is embedded, so it cannot sensibly serialize itself.

[elasticsearchmachine]

Pinging @elastic/es-distributed-indexing (Team:Distributed Indexing)

[Copilot]

Pull Request Overview

This PR refactors the serialization logic for SplitShardCountSummary by moving the serialization responsibility from the summary class itself to the containing ReplicationRequest class. The change simplifies the design by making serialization dependent on the request's transport version rather than having the summary handle its own serialization.

Key changes:

• Remove Writeable interface implementation from SplitShardCountSummary
• Add static factory method and integer conversion methods to SplitShardCountSummary
• Move transport version constants and serialization logic to ReplicationRequest

Reviewed Changes

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

File	Description
SplitShardCountSummary.java	Removes serialization capabilities and adds factory/conversion methods
ReplicationRequest.java	Takes over serialization responsibility with transport version handling

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[Copilot]

[nitpick] The constructor visibility was changed from package-private with a comment 'visible for testing' to package-private without comment. Consider adding back the visibility comment or making it private since it's now only used internally via the fromInt() factory method.

Suggested change

	SplitShardCountSummary(int shardCountSummary) {
	private SplitShardCountSummary(int shardCountSummary) {

[bcully]

I didn't mean to remove the comment. Thanks copilot!

[Copilot]

[nitpick] The field declaration was moved after the method definitions. Consider keeping field declarations at the top of the class for better readability and consistency with Java conventions.