feat: able to assign to a subscripted string

[am-cid]

closes #279 if ever the team decides to allow string mutability

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string subscripts can be assigned to

a-senpai = "1123"~
a{0} = "09 "~

pwint(a)~
>.< output: "09 123"

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source

transpiled

output

output 2

[am-cid]

Team did not have a unanimous decision. We're going to do immutable strings