ruff

bc6ea687 - [ty] Add precise iteration and unpacking inference for string literals and bytes literals (#20023)

[ty] Add precise iteration and unpacking inference for string literals and bytes literals (#20023) ## Summary Previously we held off from doing this because we weren't sure that it was worth the added complexity cost. But our code has changed in the months since we made that initial decision, and I think the structure of the code is such that it no longer really leads to much added complexity to add precise inference when unpacking a string literal or a bytes literal. The improved inference we gain from this has real benefits to users (see the mypy_primer report), and this PR doesn't appear to have a performance impact. ## Test plan mdtests