feat: add path-based configuration access methods

[devspexx]

Overview

Adds path-based configuration access to simplify loading configs without manually constructing File instances.

Changes

• Added getByPath(String path)
• Added getOrLoadByPath(String path)
• Introduced internal path resolution with cross-platform normalization
• Resolves paths relative to plugin data folder

Example

YamlConfig config = configManager.getOrLoadByPath("configs/settings.yml");