Event Lineage: Create Transform Function for All Filter

**Problem**
Transform functions are how we track changes to eventtypes as events flow through the system. To support the all filter, we should implement a transform function to represent how a given eventtype becomes "narrower" as it passes the filter. Specifically, this transform function should (for each filter in the all filter):
1. Apply the filter
2. If the resulting eventtype is `nil`, return `nil`.

**[Persona:](https://github.com/knative/eventing/blob/main/docs/personas.md)**
Which persona is this feature for?

**Exit Criteria**
A measurable (binary) test that would indicate that the problem has been resolved.

**Time Estimate (optional):**
How many developer-days do you think this may take to resolve?

**Additional context (optional)**
Add any other context about the feature request here.

Start by locating the existing transform-function entry points and the all-filter implementation in the Go codebase. Trace how each filter changes the event type, then add coverage showing that every filter is applied and that a nil result stops the transformation; done means those cases pass consistently.

Written by the indexing model from the issue text.