Clear secondary streams on primary PowerShell object

Currently we reuse the same PowerShell object for every script invocation/prompt evaluation, but we aren't clearing the streams afterward. Example:

PS> $context = $psEditor.Components.Get([Microsoft.PowerShell.EditorServices.PowerShellContext])
PS> $ps = $context.GetType().GetField('powerShell', 60).GetValue($context)
PS> $ps.Streams.Information
# <Empty>
PS> Write-Host 'first message'
PS> $ps.Streams.Information
# first message
PS> Write-Host 'second message'
PS> $ps.Streams.Information
# first message
# second message

Same for the other streams e.g. warning, verbose, debug, and progress (even though progress is not shown, the record is still stored until the end of the session)

Depending on how long the PSIC is left open and how much these streams are being written to, this could be the cause of some reported memory usage issues.

Start at the code that reuses the primary PowerShell object for script invocations and prompt evaluations, then inspect its Streams.Information, warning, verbose, debug, and progress collections. Reproduce the accumulation shown in the issue and trace when each invocation completes. Done means secondary stream records do not persist across invocations, including progress records, and the behavior is covered by the relevant tests if present.