Track casing of r-string prefixes in the tokenizer and AST #25919

Job	Run time
cargo fmt	14s
pre-commit	30s
mkdocs	2m 8s
Determine changes	10s
python package	1m 12s
cargo test (linux)	3m 52s
benchmarks	4m 26s
cargo clippy	1m 47s
cargo fuzz	5m 24s
cargo test (wasm)	1m 31s
cargo test (windows)	8m 0s
cargo udeps	1m 57s
formatter instabilities and black similarity	3m 34s
test scripts	48s
test ruff-lsp	15s
ecosystem	13m 33s
	49m 21s

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