Go bindings: enable concurrent dec_ref for GC-driven finalizers (#10002)

The Go bindings rely on finalizers to release Z3 references, which can
run during concurrent GC and trigger unsafe decref behavior in shared
contexts. This change aligns Go with other managed bindings by enabling
concurrent decref support at context creation time.

- **Context initialization**
  - Call `Z3_enable_concurrent_dec_ref` in both Go context constructors:
    - `NewContext()`
    - `NewContextWithConfig(cfg *Config)`
- This ensures AST/object finalizer decrefs are handled under Z3’s
concurrent dec-ref mode.

- **Go binding docs**
- Updated Go README memory-management section to explicitly document
that contexts enable concurrent dec-ref for finalizer-driven decref
paths.

- **Focused regression coverage**
- Added a small Go test (`z3_context_test.go`) that exercises
`NewContext` through a basic SAT flow, ensuring context construction and
normal solver usage remain consistent.

```go
func NewContext() *Context {
    ctx := &Context{ptr: C.Z3_mk_context_rc(C.Z3_mk_config())}
    C.Z3_enable_concurrent_dec_ref(ctx.ptr)
    runtime.SetFinalizer(ctx, func(c *Context) {
        C.Z3_del_context(c.ptr)
    })
    return ctx
}
```

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/api/go/README.md

@@ -310,7 +310,7 @@ go run basic_example.go
 
 ## Memory Management
 
-The Go bindings use `runtime.SetFinalizer` to automatically manage Z3 reference counts. You don't need to manually call inc_ref/dec_ref. However, be aware that finalizers run during garbage collection, so resources may not be freed immediately.
+The Go bindings use `runtime.SetFinalizer` to automatically manage Z3 reference counts. You don't need to manually call inc_ref/dec_ref. However, be aware that finalizers run during garbage collection, so resources may not be freed immediately. The bindings enable `Z3_enable_concurrent_dec_ref` when creating contexts so finalizer-driven decref operations are safe with concurrent GC.
 
 ## Thread Safety
 

src/api/go/z3.go

@@ -89,6 +89,7 @@ type Context struct {
 // NewContext creates a new Z3 context with default configuration.
 func NewContext() *Context {
 	ctx := &Context{ptr: C.Z3_mk_context_rc(C.Z3_mk_config())}
+	C.Z3_enable_concurrent_dec_ref(ctx.ptr)
 	runtime.SetFinalizer(ctx, func(c *Context) {
 		C.Z3_del_context(c.ptr)
 	})
@@ -98,6 +99,7 @@ func NewContext() *Context {
 // NewContextWithConfig creates a new Z3 context with the given configuration.
 func NewContextWithConfig(cfg *Config) *Context {
 	ctx := &Context{ptr: C.Z3_mk_context_rc(cfg.ptr)}
+	C.Z3_enable_concurrent_dec_ref(ctx.ptr)
 	runtime.SetFinalizer(ctx, func(c *Context) {
 		C.Z3_del_context(c.ptr)
 	})