feat: add multi-storage-client backend for file open

[jayya2]

This PR adds support for the Multi-Storage Client (MSC) backend to handle object storage access in Lhotse. The changes include:

Features

• New MSCIOBackend for handling MSC protocol URLs
• URL transformation from existing protocols (e.g., s3://) to MSC format via
  • LHOTSE_MSC_OVERRIDE_PROTOCOLS env for supported protocols, e.g. s3:// -> msc://
  • LHOTSE_MSC_PROFILE env for profile/bucket name overrides, e.g. msc://my-bucket -> msc://my-profile

Implementation Details

• Added URL transformation utilities for bucket/profile name handling
• Integrated MSC backend into the default IO backend chain
• Added unit tests for MSC functionality

Configuration

MSC behavior can be configured through environment variables:

• LHOTSE_MSC_OVERRIDE_PROTOCOLS: Comma-separated list of protocols to override (e.g., "s3,gs")
• LHOTSE_MSC_PROFILE: Profile name to use for bucket override

Dependencies

• Requires multistorageclient package to be installed