Three-argument filtered map macro raises ValueError during evaluation

## Summary

The standard filtered `map(x, predicate, transform)` form compiles but raises `ValueError: too many values to unpack (expected 2)` during evaluation. The equivalent `filter(...).map(...)` expression completes normally.

## Reproduction

Save the following as `repro.py`.

```python
from celpy import Environment

for expression in (
"[1,2,3].map(x, x > 1, x+1)[0]",
"[1,2,3].filter(x, x > 1).map(x, x+1)[0]",
):
env = Environment()
try:
result = env.program(env.compile(expression)).evaluate({})
print(expression, "=>", result)
except Exception as exc:
print(expression, "=>", type(exc).__name__, str(exc))
```

Run:

```sh
python -m pip install cel-python==0.5.0
python repro.py
```

## Actual result

```text
[1,2,3].map(x, x > 1, x+1)[0] => ValueError too many values to unpack (expected 2)
[1,2,3].filter(x, x > 1).map(x, x+1)[0] => 3
```

## Expected behavior and why

Both expressions should return `3`: filter `[1,2,3]` to `[2,3]`, add one to each element, and select the first result.

CEL defines `e.map(x, p, t)` as the map transformation with predicate filtering before transformation:
https://github.com/cel-expr/cel-spec/blob/ba58ae5007845f3a1279b488cdeb79645ce958bb/doc/langdef.md#macros

## Code-level observation and impact

The map evaluator unpacks two macro arguments where this form supplies three. This is an internal Python arity error rather than the normal evaluation of a supported CEL expression. If this macro overload is intentionally outside the supported profile, please clarify that scope; accepting the syntax and then raising an unpacking error is still an unhelpful failure mode for callers.

## Environment

- Package: cel-python 0.5.0
- Runtime: CPython 3.13.3
- OS: macOS 26.6.2, Apple Silicon / arm64
- Reproduced: 2026-09-11

[cel-python-reproduction.zip](https://github.com/user-attachments/files/32164148/cel-python-reproduction.zip)

Beginnen Sie damit, die bereitgestellte repro.py gegen den map-Makro-Evaluator auszuführen, und verfolgen Sie den im Issue beschriebenen gefilterten map-Pfad mit drei Argumenten. Fügen Sie Abdeckung für beide Ausdrücke hinzu und bestätigen Sie anschließend, dass die gefilterte Form 3 zurückgibt, anstatt ValueError auszulösen, während die bestehende filter(...).map(...)-Form weiterhin erfolgreich ist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.