fd_write ignores iovs_len > 1

Am I crazy? I thought I might be misunderstanding something, but then I found someone else's example online that also doesn't work.

### Test Case

```wat
;; hello.wat
(module
;; define the expected type for fd_write
(type $write_type (func (param i32 i32 i32 i32) (result i32)))
(import "wasi_snapshot_preview1" "fd_write" (func $write (type $write_type)))

;; Define a memory that is one page in size (64KiB).
(memory (export "memory") 1)

;; At offset 66 and 80 in the memory, we store the data.
(data (i32.const 66) "Hello, World!\n")
(data (i32.const 80) "Howdy!\n")


(func $main (export "_start")
;; Store the iovs
(i32.store (i32.const 0) (i32.const 66)) ;; Start of data (= *buf)
(i32.store (i32.const 4) (i32.const 14)) ;; Length of data (= buf_len)

(i32.store (i32.const 8) (i32.const 80)) ;; Start of data (= *buf)
(i32.store (i32.const 12) (i32.const 8)) ;; Length of data (= buf_len)

i32.const 1 ;; fd param. In Unix this means: 0 = stdin, 1 = stdout, 2 = stderr

;; here are different combinations possible:
;; 0,1 would read only "Hello, World!"
;; 8,1 would read only 'Howdy'
i32.const 0 ;; iovs -> Offset. Points to first iovec
i32.const 2 ;; iovs_len -> How many iovs should be read, set it to 2 to read also Howdy

i32.const 92 ;; Pointer to the place in memory where the number of written bytes shall be placed.

call $write ;; call fd_write and drop the result code
drop
)
)
```

### Steps to Reproduce

```shell
wasmtime hello.wat
```

### Expected Results

```
Hello, World!
Howdy!
```

### Actual Results

```
Hello, World!
```

### Versions and Environment

Wasmtime version or commit: `wasmtime-cli 18.0.2 (90db6e99f 2024-02-28)`

Operating system: MacOS 14.3.1

Architecture: arm64 (M1 Pro)