Add script for basic testing

## Feature
Add a script for some basic testing such as finding batch size, testing just the dataset or just the network.

## Motivation
When we are developing a new model we want to test parts of our pipeline before pursuing coding. Having a tool to just test some parts (e.g. : dataset, network creation/forward) and some setting tests before starting training (e.g. : batch size) would ease the use of the framework.

## Example of use
I imagine something like :
- `python -m bootstrap.test --batch_size 50 80 100 --options /path/to/options`
- `python -m bootstrap.test --network forward --options /path/to/options`
- `python -m bootstrap.test --dataset --options /path/to/options`

To test networks we would need datasets to generate empty items (so we don't need to load an entire dataset) so we can feed the network with batches really fast.

Use the proposed `python -m bootstrap.test` entry point and the example invocations as the starting contract. Define how batch-size checks, dataset-only checks, and network forward checks receive `/path/to/options`, including the empty-item dataset requirement. Done means the script supports these pipeline checks before training and documents the supported commands.

Written by the indexing model from the issue text.