fix: handle null positional args before matchers

[a1573595]

Status

READY

Breaking Changes

NO

Description

Fixes #256.

This fixes positional matcher reconstruction when a real nullable positional argument appears before an argument matcher.

Example:

verify(() => mock.method(null, any()));

Previously, mocktail treated any positional null as a possible matcher placeholder. That caused the real null argument to be consumed as the matcher position, shifting the actual matcher and making verification or capture fail.

The change keeps the existing fallback-value reconstruction model, but removes the blanket null shortcut. Positional matchers are now reconstructed only when the invocation argument matches a stored matcher fallback value. This preserves literal null arguments as real arguments while still supporting any() and captureAny().

Added regression coverage for:

• verifying null followed by any()
• capturing an argument after a literal null with captureAny()

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore