refactor(stash-finder): modernize file IO and CSV handling

[Big-Iron-Cheems]

Type of change

• Bug fix
• New feature

Description

Refactors StashFinder file I/O and chunk coordinate handling.

The changes modernize the CSV serialization/deserialization by defining CSV fields with explicit getters and setters,
while keeping CSV coordinates stored as chunk coordinates, matching the existing JSON representation and preserving the previous coordinate format.

Chunk world coordinates are no longer stored as redundant/transient fields.
They are derived directly from ChunkPos using Minecraft's ChunkPos helpers, ensuring there is a single source of truth for chunk position and avoiding duplicated coordinate state.

ChunkPos is also treated as effectively immutable within Chunk, reflecting that the chunk position is assigned when the stash is created and is not subsequently replaced.

Related issues

None.

How Has This Been Tested?

Tested by loading and saving existing StashFinder JSON/CSV data and verifying that:

• Chunk coordinates are preserved in their existing format.
• CSV and JSON continue to represent the same chunk positions.
• World-space coordinates are correctly derived from ChunkPos.
• Stash coordinates displayed in the UI and notifications remain correct.
• Goto and tracer functionality continue to target the center of the recorded chunk.
• Existing stash entries load correctly after the coordinate refactor.

Checklist:

• My code follows the style guidelines of this project.
• I have added comments to my code in more complex areas.
• I have tested the code in both development and production environments.