Restore lazy evaluation of fallible CASE

[findepi]

Which issue does this PR close?

• Closes Regression: eager evaluation of expressions inside CASE conditional expression #15384

Rationale for this change

Commit 0f4b8b1 (#13953) introduced a new
optimized evaluation mode for CASE expression with exactly one WHEN-THEN
clause and ELSE clause being present. Apparently, the new mode did not
take into account expensive or fallible expressions, as it
unconditionally evaluated both branches. This is definitely incorrect
for fallible expressions. For these, fallback to the original execution
mode.

What changes are included in this PR?

fix so that CASE is lazy again

Are these changes tested?

slt

Are there any user-facing changes?

yes

[findepi]

Alternatively, we could change Literal::evaluate_selection to return null scalar when selection is empty.
However, for this to be effective, it would require adding evaluate_selection implementations to any physical expressions that may contain literals. Then, using BooleanArray for selection would no longer be efficient, as expressions would need to scan it for true values, and deal with nullability. A new type for selection would likely be more appropriate. Anyway, this sounds not like a bug fix we need for the regression.

[alamb]

Thank you @findepi

Given the code was generating incorrect answers but is now correct this looks good to me. I am running some benchmarks to see if there are any performance impacts

cc @aweltsch @2010YOUY01 who authored/helped with #13953

[alamb]

I verified that this errors on main:

> SELECT v, CASE WHEN v != 0 THEN 10/v ELSE 42 END FROM (VALUES (0), (1), (2)) t(v);
+---+-------------------------------------------------------------------+
| v | CASE WHEN t.v != Int64(0) THEN Int64(10) / t.v ELSE Int64(42) END |
+---+-------------------------------------------------------------------+
| 0 | 42                                                                |
| 1 | 10                                                                |
| 2 | 5                                                                 |
+---+-------------------------------------------------------------------+
3 row(s) fetched.
Elapsed 0.002 seconds.

> SELECT v, CASE WHEN v < 0 THEN 10/0 ELSE 1 END FROM (VALUES (1), (2)) t(v);
Arrow error: Divide by zero error

[alamb]

Here are my benchmark results. My conclusion is no discernable difference

group                          findepi_lazy-case                      main
-----                          -----------------                      ----
case_when: CASE expr           1.02     25.1±0.24µs        ? ?/sec    1.00     24.6±0.27µs        ? ?/sec
case_when: column or null      1.00   1513.6±2.56ns        ? ?/sec    1.00  1518.0±34.78ns        ? ?/sec
case_when: expr or expr        1.01     33.8±0.28µs        ? ?/sec    1.00     33.4±0.16µs        ? ?/sec
case_when: scalar or scalar    1.00      8.3±0.02µs        ? ?/sec    1.00      8.3±0.09µs        ? ?/sec