chore: upgrade deps.

[morganney]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (0f7b10b) to head (c783b02).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #26   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           13        13           
  Lines          261       261           
  Branches        91        92    +1     
=========================================
  Hits           261       261           

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[Copilot]

Pull request overview

This PR upgrades the project’s Node/TypeScript toolchain dependencies and migrates ESLint configuration from legacy .eslintrc.json/.eslintignore to ESLint v9 “flat config”.

Changes:

• Bumps multiple devDependencies (ESLint 9, Jest 30, TypeScript 5.9, Duel 4).
• Replaces legacy ESLint config files with a new eslint.config.js flat configuration.
• Updates .gitignore to ignore Duel’s cache directory.

Reviewed changes

Copilot reviewed 4 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
package.json	Updates package version and upgrades devDependencies (ESLint/Jest/TypeScript/Duel), adjusting the lint toolchain dependencies.
eslint.config.js	Adds ESLint v9 flat config with ignores, globals, and recommended configs for JS/TS/Jest.
.gitignore	Ignores .duel-cache generated by the build tool.
.eslintrc.json	Removed legacy ESLint config (superseded by flat config).
.eslintignore	Removed legacy ignore file (superseded by flat config ignores).

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