docs: document compiled plugins

[mhmd-azeez]

Related to #97

This PR documents CompiledPlugin, it also adds a note clarifying the lifetime of a CompiledPlugin is tied to wazero cache if it's enabled

[johanjanssens]

@mhmd-azeez Thanks for this! Some feedback.

CompilationCache

ctx := context.Background()
cache := wazero.NewCompilationCache()
defer cache.Close(ctx)

manifest := Manifest{Wasm: []Wasm{WasmFile{Path: "wasm/noop.wasm"}}}

config := PluginConfig{
    EnableWasi:    true,
    ModuleConfig:  wazero.NewModuleConfig(),
    RuntimeConfig: wazero.NewRuntimeConfig().WithCompilationCache(cache),
}

_, err := NewPlugin(ctx, manifest, config, []HostFunction{})

This code doesn't make it clear to me that the cache lifetime extends that of the runtime. The info in the Wazero code can offer inspiration:

https://github.com/tetratelabs/wazero/blob/0dea5d7ee1de12d2817d6ac8548a4d36aaf59aea/cache.go#L64

Possible inspiration from Wazero examples: https://github.com/tetratelabs/wazero/blob/0dea5d7ee1de12d2817d6ac8548a4d36aaf59aea/examples/multiple-runtimes/counter.go

CompiledPlugin

The main reason to compile a plugin and later instantiate it is to allow for a plugin to be used across multiple goroutines as also mentioned in the code:

go-sdk/plugin.go

Line 67 in b1e59a8

// NewPlugin creates compiles and instantiates a plugin that is ready

go-sdk/plugin.go

Line 112 in b1e59a8

func NewCompiledPlugin(

The example exit, out, err := plugin.Call("count_vowels", data) would therefor best be explained by putting the Call into a goroutine, which demonstrates thread safety.

Possible inspiration from Wazero examples: https://github.com/tetratelabs/wazero/blob/0dea5d7ee1de12d2817d6ac8548a4d36aaf59aea/examples/concurrent-instantiation/main.go

Note that there is an extra caveat here that took me a off guard a bit, which is the plugin state is not shared across instances. In a concurrency scenario with multiple instances, state will be bound to the specific instance of the plugin.

[mhmd-azeez]

@johanjanssens thanks for the feedback, I have added a comment in the wazero cache section, and i have used goroutines in the compiled plugin section

[johanjanssens]

Thanks! This is looking good, ready to roll :)