fix: normalize channel names to canonical URLs using ChannelConfig

[ritankarsaha]

Description

Adds a channel_config: ChannelConfig field to SolverTask (defaulting to the standard conda.anaconda.org alias for backward compatibility) and threads it through to CondaDependencyProvider::new.

The TODO block that previously just collected channel-pinned specs is replaced by apre-computation step that maps each spec to its canonical channel URL, re-expanding short names through the caller-provided config. During per-record filtering, record.channel is likewise normalized through the same config before comparison. This ensures that a spec like my-channel::numpy correctly matches or rejects records regardless of which channel alias was active when the MatchSpec was parsed.

Fixes #2294

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added sufficient tests to cover my changes.

@baszalmstra