fix: normalize plugin version tags on download

[ahmedhesham6]

Description

Normalize plugin version resolution so download/install uses a canonical version format and retries the alternate tag form when needed.

Related Issues

None.

Changes Made

• normalize configured/latest plugin versions to a canonical v-prefixed form
• retry downloads with the alternate version form when storage/tag naming disagrees
• harden version comparisons against whitespace and V/v prefix differences
• add unit coverage for normalization, fallback toggling, and comparisons

Testing

• cargo fmt --check -- cli/src/utils/plugins.rs
• cargo clippy -p stakpak --all-targets -- -D warnings
• cargo test -p stakpak -- --nocapture
• Tested on macOS

Breaking Changes

None.

[Copilot]

Pull request overview

Normalizes plugin version resolution so downloads/installations use a canonical v-prefixed version string, while still supporting backends that store artifacts/tags without the v prefix.

Changes:

• Canonicalize configured and “latest” versions into a v-prefixed form for internal comparisons and selection.
• Add a one-time retry that flips the v prefix (v1.2.3 ↔ 1.2.3) when a download fails.
• Harden version comparison to ignore whitespace and V/v prefix differences; add unit tests for normalization and comparisons.

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