Feels like this is safe to do, since we plan to consider dropping Wasmtime for most SDKs except possibly an async-friendly Rust SDK, right?

Yeah, that's the goal, and we can always replace this with some other configuration options when we drop wasmtime, since there will be some refactoring needed at that point anyway - until then this gives users of the current Rust SDK some control over the low-level stuff that we don't necessarily need to care about.

Some of these values may be overwritten by the Extism runtime

Sorry if I'm a bit late, but I think it would be quite usefull to know which values are overwritten. I can already imagine a user changing settings and wondering why nothing is changing. From what I could quickly see, here's the spot where we overwrite some settings:

        let mut config = config.unwrap_or_default();
        config
            .async_support(false)
            .epoch_interruption(true)
            .debug_info(debug_options.debug_info)
            .coredump_on_trap(debug_options.coredump.is_some())
            .profiler(debug_options.profiling_strategy)
            .wasm_tail_call(true)
            .wasm_function_references(true)
            .wasm_gc(true);

https://github.com/extism/extism/blob/25bcbe092d94562441a2eb54a74584e023cc1e05/runtime/src/plugin.rs#L334C1-L343C28

Could we change with_wasmtime_config documentation to something like:

Configure an initial wasmtime config to be passed to the plugin

Warning: some values might be may be overwritten by the Extism runtime. In particular:

• async_support
• epoch_interruption
• debug_info
• coredump_on_trap
• profiler
• wasm_tail_call
• wasm_function_references
• wasm_gc

See the implementation details of [this function](Plugin::build_new) to check which values are overwritten.

Good idea, can you open a PR with this change?