[clang-tidy] Speed up `readability-uppercase-literal-suffix` (#178149)
As usual, this is one of our most expensive checks according to
`--enable-check-profile`.
Measuring overall runtime:
```sh
hyperfine \
--shell=none \
--prepare='cmake --build build/release --target clang-tidy' \
'./build/release/bin/clang-tidy --checks=-*,readability-uppercase-literal-suffix all_headers.cpp -header-filter=.* -system-headers -- -std=c++23 -fno-delayed-template-parsing'
```
Status quo:
```txt
Time (mean ± σ): 4.435 s ± 0.012 s [User: 4.158 s, System: 0.275 s]
Range (min … max): 4.409 s … 4.455 s 10 runs
```
With this change:
```txt
Time (mean ± σ): 3.549 s ± 0.010 s [User: 3.328 s, System: 0.223 s]
Range (min … max): 3.540 s … 3.569 s 10 runs
```
Measuring with `--enable-check-profile`:
Status quo:
```txt
---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
1.1875 (100.0%) 0.1406 (100.0%) 1.3281 (100.0%) 1.3147 (100.0%) readability-uppercase-literal-suffix
```
With this change:
```txt
---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
0.2500 (100.0%) 0.0469 (100.0%) 0.2969 (100.0%) 0.2904 (100.0%) readability-uppercase-literal-suffix
```
However, subtracting 200 ms to account for the "[`hasParent`
tax](https://github.com/llvm/llvm-project/pull/178149#discussion_r2736652174)",
the "true" numbers are probably closer to:
```
---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
Status quo: 0.9875 (100.0%) 0.1406 (100.0%) 1.1281 (100.0%) 1.1147 (100.0%) readability-uppercase-literal-suffix
With this change: 0.0500 (100.0%) 0.0469 (100.0%) 0.0969 (100.0%) 0.0904 (100.0%) readability-uppercase-literal-suffix
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