feat: implement v3 repodata/matchspec support in pixi spec

[wolfv]

Description

Adds new fields to PixiSpec types (extras, flags, license_family, condition, track_features) and switches MatchSpec parsing to v3-aware ParseMatchSpecOptions across pixi crates. The repodata reporter now surfaces a deduplicated warning when a backend reports an unsupported repodata revision.

This is the pixi-side half of v3 support; the pixi-build backend changes follow in a separate PR.

This implements the following changes to the Pixi spec syntax:

# select variant with `flags` instead of build string globs
foo = { version = "*", flags = ["release"] }

# select extra dependency groups
foo = { version = "*", extras = ["numpy", "plotting"] } 

# conditional dependencies are mainly useful for runtime dependencies of noarch packages.
foo = { version = "*", when = "__unix" }

# use `all` for "and"
foo = { version = "*", when = { all = ["python >=3.10", "numpy"] } }

# use `any` for "or"
foo = { version = "*", when = { any = ["python >=3.10", "numpy", "matplotlib"] } }

How Has This Been Tested?

You can test with the packages from this channel: https://preview-pr-2147.prefix.dev/channels/test-v3

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: Claude

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.
• I have verified that changes that would impact the JSON schema have been made in schema/model.py.

[hunger]

Why don't we need ParseStrictness anymore? Is the new default Strict enough?

[wolfv]

@hunger we use same "lenient" as before? Or where did you see that?

ParseMatchSpecOptions::lenient().with_repodata_revision(RepodataRevision::V3)

[hunger]

Sorry, I missed that ParseStrictness is now part of the ParseMatchSpecOptions.

[baszalmstra]

I thought we had the ability to attach miette style hints to these errors.