<Performance> fuzzbug: Repeated `ref.func` in a tiny hot loop is much slower in Wasmtime than in Wasmer Cranelift

## Describe the bug

Repeated `ref.func` in a tiny hot loop appears to be much slower in Wasmtime than in Wasmer Cranelift.

After reduction, I got a minimal reproducer that preserves essentially the same gap, plus two close controls where the gap disappears. The evidence points specifically to the per-iteration `ref.func` path, not to the loop scaffold or the reference sink.

[test_cases.zip](https://github.com/user-attachments/files/27424477/test_cases.zip)

Primary reproducer:
- `primary_reproducer_ref_func_hotloop.wat`

Supporting controls:
- `supporting_control_ref_func_hoisted.wat`
- `supporting_control_ref_null_hotloop.wat`

## Test Case

Primary reproducer loop body:

```wat
ref.func $f0
global.set $g0
local.get $i
i64.const 1
i64.sub
local.tee $i
i64.const 0
i64.ne
br_if $body
```

The reduced reproducer uses:
- trip count: `2^30`
- one declared function `$f0`
- one mutable `funcref` global sink
- one declarative element entry so that `ref.func` remains valid

Matched controls:
- same loop shape, but use a hoisted prebuilt non-null reference via `global.get $g0`
- same loop shape, but replace `ref.func` with `ref.null func`

## Steps to Reproduce

1. Build the primary testcase:

```bash
wat2wasm primary_reproducer_ref_func_hotloop.wat -o primary_reproducer_ref_func_hotloop.wasm
```

2. Warm up once:

```bash
wasmtime primary_reproducer_ref_func_hotloop.wasm
```

3. Measure runtime:

```bash
perf stat -r 3 -e 'task-clock' wasmtime primary_reproducer_ref_func_hotloop.wasm
```

4. Run the same flow on the two supporting controls above.

5. For comparison with Wasmer Cranelift:

```bash
wasmer run primary_reproducer_ref_func_hotloop.wasm
perf stat -r 3 -e 'task-clock' wasmer run primary_reproducer_ref_func_hotloop.wasm
```

## Expected and actual Results

### Primary reproducer and close controls

| testcase | wasmer_cranelift (s) | wasmtime (s) | ratio |
|---|---:|---:|---:|
| `primary_reproducer_ref_func_hotloop` | 2.7668 | 38.2027 | 13.81x |
| `supporting_control_ref_func_hoisted` | 0.5029 | 0.5266 | 1.05x |
| `supporting_control_ref_null_hotloop` | 0.4083 | 0.4468 | 1.09x |

Observed pattern:
- the primary reproducer is dramatically slower in Wasmtime than in Wasmer Cranelift;
- hoisting the non-null function reference out of the loop collapses the gap;
- replacing `ref.func` with `ref.null func` also collapses the gap.

This makes the trigger look very specifically tied to repeated hot-loop `ref.func`.

### Family-level consistency

The original generated `ref.func` seeds showed the same shape:

| testcase | wasmer_cranelift (s) | wasmtime (s) | ratio |
|---|---:|---:|---:|
| `ref_func_1` | 2.9594 | 38.5392 | 13.02x |
| `ref_func_2` | 2.7539 | 38.8498 | 14.11x |

A related mixed testcase from the `ref.is_null` family also showed the same gap only when the loop used `ref.func` to create the non-null input each iteration:

| testcase | wasmer_cranelift (s) | wasmtime (s) | ratio |
|---|---:|---:|---:|
| `ref_is_null_2` (`ref.func` + `ref.is_null`) | 2.9624 | 39.3673 | 13.29x |
| hoisted non-null control for `ref.is_null` | 0.6419 | 0.6855 | 1.07x |

So the `ref.is_null` outlier seems to be explained by the same repeated-`ref.func` trigger, rather than by `ref.is_null` itself.

## Versions and Environment

- Wasmtime version: `wasmtime 41.0.0 (4898322a4 2025-12-18)`
- Host OS: `Ubuntu 22.04.5 LTS x64`
- Architecture: `x86_64`
- CPU: `12th Gen Intel(R) Core(TM) i7-12700`

## Extra Info

I also checked Wasmtime CLIF for the reduced reproducer to make sure the benchmark is still alive.

The hot loop still performs a per-iteration builtin call:

```text
v6 = call fn0(v0, v32)
store notrap aligned table v6, v0+96
```

where `fn0` is `wasmtime_builtin_ref_func`.

That builtin still performs a deeper indirect runtime call with extra frame/return-address bookkeeping:

```text
v3 = get_frame_pointer.i64
store notrap aligned v3, v2+40
v4 = get_return_address.i64
store notrap aligned v4, v2+48
v7 = call_indirect sig0, v6(v0, v1)
```

In contrast, the hoisted control's hot loop is just a load/store path without `wasmtime_builtin_ref_func` in the loop:

```text
v5 = load.i64 notrap aligned table v0+96
store notrap aligned table v5, v0+112
```

I have not confirmed the internal root cause, so I’m only reporting the measured trigger pattern:
- repeated `ref.func` in a tiny hot loop;
- slowdown remains after reduction to a minimal reproducer;
- the gap disappears when `ref.func` is removed from the loop;
- the gap also disappears for repeated `ref.null func`.