Remove unused internal functions

[nohwnd]

Draft, and stacked on #2906. It branches off that PR, so until #2906 merges the diff here shows both changes, review this one after that lands and it rebases clean.

While generating a full coverage report I noticed a chunk of the missed lines are not gaps, they are internal functions that nothing calls anymore. This removes 51 of them. Each one has no callers in src or tst (checked case insensitively, ignoring comments and its own definition), and none are exported.

By group:

• Old v4 assertion messages. The orphaned Should<Name>FailureMessage / NotShould<Name>FailureMessage pairs for BeGreaterThan, BeIn, BeLessThan, BeLike, BeLikeExactly, BeOfType, BeTrueOrFalse, Contain and HaveCount, plus Get-FailureMessage. The operators build the message inline now. Be, Match and FileContentMatch still call theirs so they stay. Exist and Throw also stay, because Should.Tests.ps1 asserts their message functions exist (it builds the names as strings, so a plain grep does not see that use).
• Unfinished pretty printer in Format.ps1. Format-Object, Format-Hashtable, Format-Dictionary, Get-DisplayProperty. Format-Nicely returns the value as a string and the advanced path is commented out.
• Orphaned helpers across Mock, RSpec, Runtime, Coverage, Debugging and Utility: Run-Test, Merge-CommandCoverage, Show-ParentList, Add-MockBehavior, FindMock, LastThat, Test-IsClosure, Reset-ConflictingParameters, New-BlockWithoutParameterAliases, New-OneTimeBlockSetup, Set-CurrentBlock, Reset-TestSuiteTimer, New-DiscoveredBlockContainerObject, Get-SessionStateHint, Assert-RunInProgress, and the Pester.Utility dictionary helpers.

Verification

Full test.ps1 run passes (P tests and Pester tests, 2606 passed, 0 failed). Every touched file parses.

Notes for review

• I removed by AST extent, so the diff is whole functions only.
• Sort-Property in Format.ps1 is now only reachable from the removed Get-DisplayProperty, so it is dead too, I left it in this pass, easy to drop as a follow up.
• A couple of things surfaced that are worth a look but out of scope here: PostProcess-RspecTestRun and Remove-RSpecNonPublicProperties are defined with lowercase Rspec but called with RSpec/RSPec, they only work because PowerShell is case insensitive. ConvertTo-PesterResult has no production caller, it is kept because a test uses it as the canary for "internals do not leak to the SUT".

[fflaten]

Quick reminder that we support [ExcludeFromCodeCoverage()] if we want to keep some of these while fixing CC.

New-OneTimeBlockSetup

Both OneTimeBlockSetup/-Teardown functions + public properties in Pester.Block are dead code AFAIK. EachBlockSetup and EachBlockTeardown are only called by runtime tests also. Any plans for them or should they've been removed in 6.0.0 (should be fine in 6.1.0 as well - very minor breaking change)

[nohwnd]

Yeah they're dead. The New-*Block* functions are only called from the runtime tests, so the four Pester.Block properties are never set in a real run and the two reads in Invoke-Test are no-ops. Removed all of it in #2908 (stacked on this), the functions, the properties and the reads. Kept the plugin block lifecycle steps (OneTimeBlockSetupStart etc.), those are live. All truly dead so I just deleted them instead of using [ExcludeFromCodeCoverage()].