Don't require a verifiable mock that an inner-scope default mock shadows

[nohwnd]

Fix #2672

A mock marked -Verifiable in an outer scope (Describe/Context) that you then override with another mock for the same command in an inner scope (It) could never pass Should -InvokeVerifiable: the inner mock handled the call, but Get-VerifiableBehaviors still collected the outer one and reported it as never invoked.

Get-VerifiableBehaviors now walks the scopes from the test outwards and drops a verifiable behavior when a closer scope has a default mock (one without a -ParameterFilter) for the same command - that default catches every call, so the outer behavior can't run and shouldn't be required. A verifiable mock that isn't shadowed like that is still required, same as before.

[nohwnd]

Picked this back up. Merged main in, no conflicts, and it still does what it says.

The repro in #2672 is missing the outer Mock line, so I reconstructed it and checked several shapes against released 6.1.0 and against this branch:

	6.1.0	this branch
outer verifiable in Context BeforeAll, inner verifiable in It	fails	passes
outer verifiable, inner not verifiable	fails	passes
outer verifiable at Describe level, inner default	fails	passes

One shape I got wrong on the first try, worth writing down so nobody else chases it: an outer verifiable mock with a -ParameterFilter and an inner default mock. That looks like it should be dropped too, but the call returns outer, not inner, because a parameterized behavior wins over a default one regardless of which scope it came from. So the outer mock does run there and requiring it is correct. Not a gap.

Also worth knowing: the bug only shows when the outer verifiable mock is never invoked before the overriding test. If an earlier It in the same Context already called it, the behavior is marked invoked and the override test passes even on 6.1.0. That is why a casual repro can look fine.

tst/Pester.Mock.RSpec.ts.ps1 40/40 and tst/functions/Mock.Tests.ps1 263/263 green.

Marking ready for review.

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