Fix dataloader normalization edge cases and tensor conversion robustness (fixes #145)

[kamalahasiniburra]

…ess (fixes #145)## Summary
Addresses Issue #145. This PR adds robust dataloader utilities that handle normalization edge cases and tensor conversion issues.

Features

• safe_to_tensor(): Safely converts lists, scalars, non-contiguous arrays, handles NaN/Inf
• • robust_normalize(): Handles constant images (zero variance), NaN inputs, per-channel normalization
• • create_data_pipeline(): Composable transform pipeline
• • validate_batch(): Validates batch for NaN/Inf, shape mismatches, label count mismatches
• • 18 comprehensive tests covering all edge cases
    Closes Dataloader normalization edge case and tensor conversion robustness #145