Add `prep` Sub-command for Valhalla Tile Generation

[thehoneymad]

Description:
We need to add a new sub-command named prep to our CLI. The purpose of this sub-command is to generate Valhalla tiles from the provided data. There are two possible approaches:

1. Local Option: Use the 350MB Bangladeshi OSM data available in the data/osm folder. Write Rust code to download Valhalla, then utilize Mjolnir locally to produce a tileset.

2. Docker Option: Use the same OSM data to produce the tileset in a Valhalla Docker container. A sample setup can be referenced from gis-ops/docker-valhalla.

Regardless of the path chosen, the sub-command should be written in Rust and integrated under our existing CLI.

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Acceptance Criteria:

• Add a new prep sub-command to the CLI.
• The sub-command should use Mjolnir to generate Valhalla tiles from the OSM data stored in data/osm.
• Two approaches should be supported:
  • Local Execution: Rust code must manage the download and execution of Valhalla and Mjolnir locally to generate the tileset.
  • Docker Execution: The sub-command should also support generating tiles inside a Valhalla Docker container.
• Ensure that relevant logs and progress indicators are displayed during the tile generation process.
• Provide clear documentation in the README on how to use the prep sub-command for both local and Docker options.
• Add automated tests to validate that the prep command works as expected in both local and Docker environments.

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Additional Resources:

• Reference Docker setup: gis-ops/docker-valhalla.
• Refererence of Mjolinir for tile generation: Mjolinir-Getting Started