Limit max encodings to 256 and raise error #4462

Job	Run time
build native	14m 38s
build jvm	7m 1s
ruby/spec on CRuby 3.0	3m 26s
lint	12m 46s
ruby/spec on CRuby 3.1	3m 26s
ruby/spec on CRuby 3.2	2m 56s
fast specs	1m 58s
test integration	8m 46s
specs :truffle	8m 51s
specs :language :core	12m 13s
specs :library :cext :security :command_line :tracepoint	8m 35s
test native	3m 8s
run MRI tests on native	14m 56s
	1h 42m 40s

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