Turn tomli into an optional dependency

[mwouts]

My attempt to add tomli as a (conditional) dependency to the conda package failed at https://github.com/mwouts/itables-feedstock/, so I will make it an optional dependency instead.

[github-actions]

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[Copilot]

Pull Request Overview

This PR makes the tomli library an optional dependency instead of a required one to resolve conda package issues. The change allows ITables to function without TOML config file support when tomli is unavailable.

• Move tomli from core dependencies to optional config extra
• Add graceful fallbacks when TOML parsing is unavailable
• Update version to 2.5.1 with changelog entry

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
pyproject.toml	Moves tomli from dependencies to optional config extra
src/itables/config.py	Adds fallback handling when tomllib/tomli are unavailable
src/itables/version.py	Bumps version to 2.5.1
docs/changelog.md	Documents the change in version 2.5.1

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.12%. Comparing base (7829cb5) to head (f60135c).

Files with missing lines	Patch %	Lines
src/itables/config.py	50.00%	2 Missing ⚠️

❌ Your project status has failed because the head coverage (91.39%) is below the target coverage (93.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #436      +/-   ##
==========================================
- Coverage   94.22%   94.12%   -0.10%     
==========================================
  Files          43       43              
  Lines        1869     1873       +4     
==========================================
+ Hits         1761     1763       +2     
- Misses        108      110       +2     

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