feat: add WASI Preview 1 stubs for wasip1-targeting languages

[djgilcrease]

Description of Changes

Summary

Add minimal WASI Preview 1 stub implementations so that modules compiled to wasip1 (e.g. Go with -buildmode=c-shared) can be instantiated and run in SpacetimeDB's wasmtime
runtime.

• Add wasi_stubs.rs with stub implementations for wasi_snapshot_preview1 imports (fd_write, clock_time_get, random_get, proc_exit, args_sizes_get, environ_sizes_get,
  sched_yield, etc.)
• Link the stubs into the wasmtime linker during module setup
• Call _initialize/_start exports (WASI reactor/command convention) before preinit functions to initialize the guest language runtime

Why

Languages like Go use //go:wasmimport for WASI functions, which must be satisfied by the host. Without these stubs, wasmtime fails to instantiate wasip1-targeting modules because
the wasi_snapshot_preview1 imports are unresolved. The C++ SDK handles this differently by embedding shims in the compiled module itself
(crates/bindings-cpp/src/abi/wasi_shims.cpp), but Go (and potentially other languages) require host-side stubs.

This is a prerequisite for the Go server SDK but is language-agnostic — any wasip1-targeting language benefits from these stubs.

This can also replace the stubs that were added separately for C # and C++, so those and Go can all share the same stubs. I did not update the C# and cpp modules to use these stubs in this MR as I want it to be as minimal as possible so I could start using my go server module asap.

What the stubs do

Function	Behavior
fd_write	Redirects stdout/stderr to host logger (log::info! / log::warn!)
clock_time_get	Returns real wall-clock time (Go panics on zero)
random_get	Fills buffer with pseudo-random bytes
args_sizes_get / args_get	Returns argc=0, no args
environ_sizes_get / environ_get	Returns no environment variables
poll_oneoff	Reports all subscriptions as ready
proc_exit / sched_yield	No-op
fd_close / fd_seek / fd_read / fd_fdstat_get / fd_fdstat_set_flags / fd_prestat_get / fd_prestat_dir_name	Returns ERRNO_BADF or ERRNO_NOSYS

Impact on existing modules

None. These changes are purely additive:

• The WASI stubs only add new linker functions in the wasi_snapshot_preview1 namespace, which existing Rust/C# modules don't import
• The _initialize/_start detection is a no-op for modules that don't export them

API and ABI breaking changes

None

Expected complexity level and risk

1 - very low complexity and risk, the stubs are not used by anything, BUT will enable me to externalize a go-sdk for server modules

Testing

ran the full test suite locally