Add edge case tests for cooldown bypass via top-level pin in dependency graph

[LalatenduMohanty]

Follow-up to #1153. The fix in resolve_package_cooldown() bypasses cooldown for transitive dependencies when a top-level exact pin exists in the dependency graph. The current tests cover the happy path but several edge cases need coverage to prevent regressions.

Test cases to add

1. Non-exact top-level entry does not bypass cooldown
   Graph has test-pkg>=1.0 as TOP_LEVEL (not an exact == pin). The _has_equality_pin check on the graph edge should prevent bypass, and cooldown should be enforced normally.

2. Wildcard equality pin does not bypass cooldown
   Graph has test-pkg==1.* as TOP_LEVEL. This is not a true exact pin — _has_equality_pin rejects wildcards. Cooldown should be enforced.

3. Name normalization across requirement and graph
   Transitive requirement uses Test_Pkg>=1.0 while graph has the entry under test-pkg. get_outgoing_edges canonicalizes both sides, so the bypass should still work.

4. Top-level pin takes precedence over per-package min_release_age override
   Package has resolver_dist.min_release_age: 30 in its settings, but also has a top-level == pin in the graph. The graph bypass runs before the per-package check, so the pin wins and cooldown is bypassed entirely. This is the correct precedence — an explicit pin is a stronger trust signal than a per-package cooldown override.

[LalatenduMohanty]

Adding these tests to #1157