Redesign Creator pattern for repository operations

## Overview

Redesign the `Creator` pattern used in repository operations for better consistency and type safety.

## Background

Current `Creator` classes (e.g., `SessionSchedulingHistoryCreator`, `DeploymentHistoryCreator`) have some inconsistencies:

- `fields_to_store()` method returns `dict[str, Any]` which loses type information
- Serialization logic (e.g., Pydantic model_dump) is embedded in Creator
- No clear separation between input validation and storage transformation

## Goals

- Improve type safety in Creator pattern
- Standardize serialization approach across all Creator classes
- Consider alignment with Querier/Purger patterns for consistency

## Scope

Affected Creator classes:

- `SessionSchedulingHistoryCreator`
- `KernelSchedulingHistoryCreator`
- `DeploymentHistoryCreator`
- `RouteHistoryCreator`
- Other existing Creator classes in the codebase

## Parent Epic

BA-3060

JIRA Issue: BA-3338