## Summary
The resulting type when multiplying a string literal by an integer
literal is one of two types:
- `StringLiteral`, in the case where it is a reasonably small resulting
string (arbitrarily bounded here to 4096 bytes, roughly a page on many
operating systems), including the fully expanded string.
- `LiteralString`, matching Pyright etc., for strings larger than that.
Additionally:
- Switch to using `Box<str>` instead of `String` for the internal value
of `StringLiteral`, saving some non-trivial byte overhead (and keeping
the total number of allocations the same).
- Be clearer and more accurate about which types we ought to defer to in
`StringLiteral` and `LiteralString` member lookup.
## Test Plan
Added a test case covering multiplication times integers: positive,
negative, zero, and in and out of bounds.
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Co-authored-by: Alex Waygood <alex.waygood@gmail.com>
Co-authored-by: Carl Meyer <carl@astral.sh>
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