fix: handle OR-range unions in subset() (#703)

[abhu85]

Summary

Fixes #703

subset('>=17.2.0', '^17.2.0 || >17') incorrectly returns false.

The root cause is that subset() checks each OR-branch of the dom range independently. No single branch of ^17.2.0 || >17 covers >=17.2.0 on its own, but their union does:

^17.2.0  →  [17.2.0, 18.0.0)
>17      →  [18.0.0, ∞)
union    →  [17.2.0, ∞)  ⊇  [17.2.0, ∞)  ✓

Approach

When no single dom OR-branch covers a sub comparator set, fall back to an interval-sweep algorithm:

1. Extract [lower, upper) bounds from the sub and every dom OR-branch
2. Sort dom intervals by lower bound (ties broken by operator strictness)
3. Sweep left-to-right: start at sub's lower bound and greedily extend coverage through overlapping/adjacent dom intervals
4. If the sweep reaches or exceeds sub's upper bound, the union covers the sub

Key details:

• Prerelease adjacency: <18.0.0-0 and >=18.0.0 are treated as adjacent in non-prerelease mode (no release version exists between them)
• Null-set branches (e.g., >5.0.0 <3.0.0) are detected and skipped
• * / ANY bounds are handled as [-∞, +∞)
• The fallback only activates when dom has multiple OR-branches

Test plan

• Original bug: subset('>=17.2.0', '^17.2.0 || >17') now returns true
• 42 new test cases covering: multi-branch unions, gaps, overlapping intervals, prerelease adjacency, null-set branches, * ranges, inclusive/exclusive bounds, includePrerelease option
• All existing tests continue to pass (no regressions)
• 100% code coverage (statements, branches, functions, lines)
• Lint passes

[owlstronaut]

This bypasses the prerelease-tuple admission rule that simpleSubset enforces above. So subset('>=1.0.0-pre', '<2.0.0 || >=1.0.0') will return true in non-includePrerelease mode

[owlstronaut]

Adding negative tests here for the prerelease lower/upper bounds in non-includePrerelease mode would be great to make sure a regression doesn't happen.

[owlstronaut]

eq-only branches are dropped here, so a singleton like 2.0.0 can't bridge <2.0.0 and >2.0.0 in the union