immutable instance of a struct can be modified via interface

[syobocat]

Describe the bug

I don't know whether this is a bug or a feature, but the following syntax passes compilation, allowing you to modify an immutable instance of a struct:

foo := Struct{}
mut bar := Interface(foo)

Reproduction Steps

https://play.vlang.io/p/f79078e38a

interface Interface {
mut:
	foo string
}

struct Struct {
mut:
	foo string
}

// Immutable variable
bar := Struct{
	foo: 'hello'
}

// You can't do:
/*
mut foobar := &bar
foobar.foo = 'bye'
*/

// But you can do:
mut foobar := Interface(bar)
foobar.foo = 'bye'

// Both prints `bye`
println(foobar.foo)
println(bar.foo)

Expected Behavior

Compilation error?

Current Behavior

Compiles and runs normally

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.9 5dd28cf

Environment details (OS name and version, etc.)

V full version	V 0.4.9 c4aaa2e.5dd28cf
OS	macos, macOS, 15.2, 24C101
Processor	8 cpus, 64bit, little endian, Apple M3
Memory	0.59GB/16GB
V executable	/Users/syobon/.v/v
V last modified time	2025-01-18 11:18:26
V home dir	OK, value: /Users/syobon/.v
VMODULES	OK, value: /Users/syobon/.vmodules
VTMP	OK, value: /tmp/v_501
Current working dir	OK, value: /Users/syobon
Git version	git version 2.39.5 (Apple Git-154)
V git status	weekly.2025.1-74-g5dd28cf9
.git/config present	true
cc version	Apple clang version 16.0.0 (clang-1600.0.26.6)
gcc version	Apple clang version 16.0.0 (clang-1600.0.26.6)
clang version	Apple clang version 16.0.0 (clang-1600.0.26.6)
tcc version	tcc version 0.9.28rc 2024-02-05 HEAD@105d70f7 (AArch64 Darwin)
tcc git status	thirdparty-macos-arm64 713692d4
emcc version	N/A
glibc version	N/A

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[huly-for-github]

Connected to Huly®: V_0.6-21938

[jorgeluismireles]

Let alone the interface, unsafe also permits to modify the mutable field of a non mutable object:
https://play.vlang.io/p/44c9430b7c

struct Struct {
mut:
	foo string
}
// Immutable variable
bar := Struct{ foo: 'hello' }
unsafe {
	bar.foo = 'bye'
}
println(bar.foo) // prints 'bye'

Also, I don't know if is a feature or bug.