fix(deps): read pyproject.toml with tomllib instead of tomlkit

[tiran]

Pull Request Description

What

get_pyproject_contents() only reads [build-system], so it does not need tomlkit's format-preserving parser. tomlkit (0.15.1) rejects some spec-valid files that re-open a super-table out of order, failing builds for affected packages (e.g. geventhttpclient). stdlib tomllib parses them correctly and is always available (Python >= 3.12).

Why

Closes: #1356

• PR follows CONTRIBUTING.md guidelines

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🧰 Additional context used

📚 Code guidelines (1)

AGENTS.md — auto-discovered

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Repository: python-wheel-build/fromager/.coderabbit.yaml
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• Run ID: d6c884db-5f8f-4ef4-b102-d20049e82eef

📥 Commits

Reviewing files that changed from the base of the PR and between 3d0038c and a2c053d.

📒 Files selected for processing (2)

• src/fromager/dependencies.py
• tests/test_dependencies.py

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📝 Walkthrough

Walkthrough

get_pyproject_contents now uses the standard-library tomllib parser instead of tomlkit. A regression test checks that it reads build-system requirements from a valid TOML file that reopens a table.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to a2c05

The parser change addresses valid TOML files rejected by the previous parser. No merge-blocking issue is established.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the change: replacing tomlkit with tomllib to read pyproject.toml.
Description check	✅ Passed	The description explains the parser change, the reason for it, and the linked issue.
Linked Issues check	✅ Passed	Issue #1356 requires Fromager to parse the affected spec-valid pyproject.toml. get_pyproject_contents() now uses tomllib.loads, and the regression test covers out-of-order table reopening and ve…
Out of Scope Changes check	✅ Passed	The parser replacement and regression test both directly address issue #1356. The diff shows no unrelated changes.

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