chore(deps): update wasmtime to v21 (major) (#172)

[![Mend Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [wasmtime](https://togithub.com/bytecodealliance/wasmtime) | workspace.dependencies | major | `20.0.1` -> `21.0.0` |
| [wasmtime-wasi](https://togithub.com/bytecodealliance/wasmtime) | workspace.dependencies | major | `20.0.1` -> `21.0.0` |

---

### Release Notes

<details>
<summary>bytecodealliance/wasmtime (wasmtime)</summary>

### [`v21.0.0`](https://togithub.com/bytecodealliance/wasmtime/blob/HEAD/RELEASES.md#2100)

[Compare Source](https://togithub.com/bytecodealliance/wasmtime/compare/v20.0.2...v21.0.0)

Released 2024-05-20

##### Added

-   The `wasmtime explore` subcommand now supports `*.wat` files.
    [#&#8203;8314](https://togithub.com/bytecodealliance/wasmtime/issues/8314)

-   Wasmtime now supports DWARF Fission `*.dwp` files.
    [#&#8203;8055](https://togithub.com/bytecodealliance/wasmtime/issues/8055)

-   The `wasmtime` crate now supports `#![no_std]`, and more information about
    this transition can be found in
    [#&#8203;8341](https://togithub.com/bytecodealliance/wasmtime/issues/8341).
    [#&#8203;8463](https://togithub.com/bytecodealliance/wasmtime/issues/8463)
    [#&#8203;8483](https://togithub.com/bytecodealliance/wasmtime/issues/8483)
    [#&#8203;8485](https://togithub.com/bytecodealliance/wasmtime/issues/8485)
    [#&#8203;8528](https://togithub.com/bytecodealliance/wasmtime/issues/8528)
    [#&#8203;8533](https://togithub.com/bytecodealliance/wasmtime/issues/8533)

-   A `Config` knob is now available for one-entry `call_indirect` caching to
    speed up modules with lots of `call_indirect` instructions.
    [#&#8203;8509](https://togithub.com/bytecodealliance/wasmtime/issues/8509)

-   Cranelift's riscv64 backend has initial support for the Zfa Extension.
    [#&#8203;8536](https://togithub.com/bytecodealliance/wasmtime/issues/8536)

-   The WebAssembly `tail-calls` proposal is now enabled by default when using the
    Cranelift backend, except for the s390x architecture.
    [#&#8203;8540](https://togithub.com/bytecodealliance/wasmtime/issues/8540)

##### Changed

-   Support for NaN canonicalization on x64 has been optimized to avoid branches.
    [#&#8203;8313](https://togithub.com/bytecodealliance/wasmtime/issues/8313)

-   The `bindgen!` macro now defaults to assuming imports cannot trap, but this
    behavior is configurable at macro-generation time.
    [#&#8203;8310](https://togithub.com/bytecodealliance/wasmtime/issues/8310)

-   The `fd_{read,write}` implementations in wasmtime-wasi have been optimized.
    [#&#8203;8303](https://togithub.com/bytecodealliance/wasmtime/issues/8303)

-   The `wasmtime-wasi-http` crate has been refactored and has improved
    documentation.
    [#&#8203;8332](https://togithub.com/bytecodealliance/wasmtime/issues/8332)
    [#&#8203;8347](https://togithub.com/bytecodealliance/wasmtime/issues/8347)

-   Unused `with` parameters in `bindgen!` now generate an error.
    [#&#8203;8371](https://togithub.com/bytecodealliance/wasmtime/issues/8371)

-   The `fd_read` implementation in wasmtime-wasi now only reads into a single
    iovec per call.
    [#&#8203;8415](https://togithub.com/bytecodealliance/wasmtime/issues/8415)

-   The `wasmtime_val_t` type in the C API no longer holds any allocations. This
    type must still be manually managed to properly unroot values, however.
    [#&#8203;8451](https://togithub.com/bytecodealliance/wasmtime/issues/8451)

-   Add an optimized "sleep" path for `poll_oneoff` to wasmtime-wasi.
    [#&#8203;8429](https://togithub.com/bytecodealliance/wasmtime/issues/8429)

-   The Wasmtime-internal `wasmtime-runtime` crate has been removed.
    [#&#8203;8501](https://togithub.com/bytecodealliance/wasmtime/issues/8501)

-   The pooling allocator now allows twice as many elements as before.
    [#&#8203;8527](https://togithub.com/bytecodealliance/wasmtime/issues/8527)

-   Using CMake to build the C API has been improved along a number of axes.
    [#&#8203;8490](https://togithub.com/bytecodealliance/wasmtime/issues/8490)
    [#&#8203;8497](https://togithub.com/bytecodealliance/wasmtime/issues/8497)
    [#&#8203;8549](https://togithub.com/bytecodealliance/wasmtime/issues/8549)

##### Fixed

-   Pooling allocator CLI options are now respected with the `wasmtime serve`
    subcommand.
    [#&#8203;8525](https://togithub.com/bytecodealliance/wasmtime/issues/8525)

***

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about these updates again.

---

 - [ ] If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Mend Renovate](https://www.mend.io/free-developer-tools/renovate/). View repository job log [here](https://developer.mend.io/github/andrzejressel/pulumi-wasm).