deps(python): bump regex from 2025.8.29 to 2026.2.28 in /backend

[dependabot]

Bumps regex from 2025.8.29 to 2026.2.28.

Changelog

Sourced from regex's changelog.

Version: 2026.2.28

Replaced atomic operations with mutex on pattern object for free-threaded Python.

Version: 2026.2.26

PR [#598](https://github.com/mrabarnett/mrab-regex/issues/598): Fix race condition in storage caching with atomic operations.
Replaced use of PyUnicode_GET_LENGTH with PyUnicode_GetLength.

Version: 2026.2.19

Added \z as alias of \Z, like in re module.
Added prefixmatch as alias of match, like in re module.

Version: 2026.1.15

Re-uploaded.

Version: 2026.1.14

Git issue 596: Specifying {e<=0} causes ca 210× slow-down.
Added RISC-V wheels.

Version: 2025.11.3

Git issue 594: Support relative PARNO in recursive subpatterns.

Version: 2025.10.23

'setup.py' was missing from the source distribution.

Version: 2025.10.22

Fixed test in main.yml.

Version: 2025.10.21

Moved tests into subfolder.

Version: 2025.10.20

Re-organised files.
Updated to Unicode 17.0.0.

Version: 2025.9.20

... (truncated)

Commits

• df2d5ac Replaced atomic operations with mutex on pattern object for free-threaded Pyt...
• ed3d9ca Replaced use of PyUnicode_GET_LENGTH with PyUnicode_GetLength.
• 28dd3e7 Merge pull request #598 from kevmo314/fix-storage-caching-race
• 9789c22 Added \z as alias of \Z, like in re module.
• 234de9a Re-uploaded.
• 1bc3d1e Merge branch 'hg' of https://github.com/mrabarnett/mrab-regex into hg
• d7f7c8c Git issue 596: Specifying {e<=0} causes ca 210× slow-down
• 35b2934 Merge pull request #599 from justeph/ci-add-riscv64-support
• af2f411 ci: add riscv64 manylinux/musllinux wheels
• cd631d8 Fix race condition in storage caching with atomic operations
• Additional commits viewable in compare view

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Summary by cubic

Upgrade regex to 2026.2.28 in the backend to pick up threading fixes and align with recent CPython changes. This version fixes a storage caching race, replaces atomic ops with mutexes for free-threaded Python, and adds \z and prefixmatch aliases.

^{Written for commit 1db15bb. Summary will update on new commits.}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cubic-dev-ai]

No issues found across 2 files