Switches default random source to deterministic (#736)

This changes the default random source to provide deterministic values
similar to how nanotime and walltime do. This also prevents any worries
about if wasm can deplete the host's underlying source of entropy.

Signed-off-by: Adrian Cole <adrian@tetrate.io>

config_test.go

@@ -2,6 +2,7 @@ package wazero
 
 import (
 	"context"
+	"crypto/rand"
 	"io"
 	"io/fs"
 	"math"
@@ -479,6 +480,23 @@ func TestModuleConfig_toSysContext(t *testing.T) {
 				testFS2, // fs
 			),
 		},
+		{
+			name:  "WithRandSource",
+			input: base.WithRandSource(rand.Reader),
+			expected: requireSysContext(t,
+				math.MaxUint32, // max
+				nil,            // args
+				nil,            // environ
+				nil,            // stdin
+				nil,            // stdout
+				nil,            // stderr
+				rand.Reader,    // randSource
+				&wt, 1,         // walltime, walltimeResolution
+				&nt, 1, // nanotime, nanotimeResolution
+				nil, // nanosleep
+				nil, // fs
+			),
+		},
 	}
 
 	for _, tt := range tests {