support error in session state machine apply command

[somdoron]

No description provided.

[Copilot]

Pull Request Overview

This PR adds error handling support to the session state machine's applyCommand method. Commands can now fail with user-defined errors, which are cached to maintain idempotency semantics.

Key changes:

• Introduces a new type parameter E across the session state machine APIs to represent error types
• Updates the cache schema to store Either[E, R] instead of just R, allowing both successful responses and errors to be cached
• Adds a new RequestError.UserError(e: E) case to represent command execution failures

Reviewed Changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
session-state-machine/src/main/scala/zio/raft/sessionstatemachine/package.scala	Adds error type parameter to StateWriter and RequestError; updates schema types
session-state-machine/src/main/scala/zio/raft/sessionstatemachine/SessionStateMachine.scala	Implements error handling in handleClientRequest to cache and return errors
session-state-machine/src/main/scala/zio/raft/sessionstatemachine/SessionCommand.scala	Adds E type parameter to command types
session-state-machine/src/main/scala/zio/raft/sessionstatemachine/ScodecSerialization.scala	Updates type signatures with error parameter
session-state-machine/src/main/scala/zio/raft/sessionstatemachine/Codecs.scala	Updates codec signatures for new type parameter
session-state-machine/src/test/scala/**/*.scala	Updates test files with Nothing error type and adds new error caching test
kvstore/src/main/scala/zio/kvstore/*.scala	Updates KV store implementation to use Nothing error type
.specify/templates/plan-template.md	Unrelated documentation update for project workflow

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[Copilot]

Pull Request Overview

Copilot reviewed 19 out of 19 changed files in this pull request and generated 21 comments.

Comments suppressed due to low confidence (1)

session-state-machine/src/main/scala/zio/raft/sessionstatemachine/package.scala:200

• The type parameter order Schema[E, R, SR, UserSchema] is inconsistent with SessionSchema[R, SR, E]. For better clarity and consistency, consider reordering to Schema[R, SR, E, UserSchema] to match the parameter order of SessionSchema.

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[Copilot]

Pull Request Overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 1 comment.

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