Use interpolated string handler to reduce allocations on the happy path

[vbreuss]

From this comment in #909: Use string interpolation handlers to reduce the allocation of Func<> on the happy path.

[vbreuss]

@viceroypenguin
If I understand the mechanics correctly, when using string interpolation handlers, I would have to check the condition twice:
Once, to know it myself (if it is a success or failure case) and once for the string interpolation handler.

Is this correct or did I overlook something?