…(`RUF055`) (#23634)

## Summary

Fixes #23629.

`re.split("", s)` is flagged by RUF055 and auto-fixed to `s.split("")`,
but `str.split("")` raises `ValueError: empty separator` while
`re.split("", s)` succeeds (returning `["", "a", "b", "c", ""]`). The
same applies to bytes (`rb""`).

This adds a guard to skip the diagnostic when the separator pattern is
an empty string or bytes literal specifically for `re.split` calls.
Other `re` functions (`sub`, `match`, `search`, `fullmatch`) are not
affected — their `str` equivalents all handle empty strings
equivalently.

## Test Plan

Added test cases for empty string and bytes patterns in `RUF055_0.py`
and `RUF055_3.py`. Verified that no diagnostics are emitted for these
cases and all existing RUF055 snapshot tests continue to pass:

```
cargo test -p ruff_linter -- "preview_rules::rule_unnecessaryregularexpression"
test result: ok. 4 passed; 0 failed; 0 ignored
```

* main: (30 commits)
  [ty] Introduce `types::bool`, `types::context_manager` and `types::iteration` (#23681)
  [ty] Move `KnownInstanceType`, and related types, to a new `known_instance.rs` submodule (#23680)
  [ty] Add `invalid-enum-member-annotation` lint rule (#23648)
  [`ruff`] Fix false positive for `re.split` with empty string pattern (`RUF055`) (#23634)
  [ty] Move `UnionType` and `IntersectionType` to a new `types::set_theoretic` submodule (#23678)
  [ty] Add unbound type variable detection in annotations (#23641)
  [ty] Remove `specialize_constrained` from constraint set module (#23677)
  [ty] Add partial support and validation for `Unpack` when used with tuple types (#23651)
  Update prek dependencies (#23661)
  [ty] make `StaticClassLiteral::explicit_bases` converge better in cycles (#23601)
  Improvements to CLAUDE.md (#23633)
  [ty] Move subscript logic out of `builder.rs` (#23653)
  Update Artifact GitHub Actions dependencies (#23676)
  Update actions/attest-build-provenance to 4.1.0 (#23654)
  Update Rust crate clearscreen to v4.0.5 (#23664)
  fix renovate `actions/*-artifact` updates (#23675)
  Update Rust crate clap to v4.5.60 (#23663)
  Update Rust crate unicode-ident to v1.0.24 (#23668)
  Update Rust crate anyhow to v1.0.102 (#23662)
  Update Rust crate pyproject-toml to v0.13.7 (#23666)
  ...