L1VM - immutable strings

I did add a set a string as immutable interrupt to L1VM. So a “write” access to a immutable string gives a runtime error.

L1VM (3.0.7)
	I did add a new interrupt to set strings as immutable:

	(set string s worldstr " world!")

	// set string as immutable:
	string_immutable (worldstr)

	See "intr.l1h"!

-- Stefan Pietzonke <info@midnight-coding.de> Mon 18 Mar 2024 04:32  +010

This should work on all string module functions.

Have fun!