Harden tests and modernize package metadata

[mxkh72]

Summary

• harden failure-path tests so expected throws are enforced
• remove force-cast from tests and replace with safe assertions
• modernize package/docs metadata by moving to swift-tools-version:5.10 and removing the stale Carthage support claim
• preserve the existing Requirement.isValid design (non-throwing, returns false when validation throws)
• add targeted tests for previously untested paths in Requirement and Check.nonEmpty
• increase core package coverage to 100% for Requirement.swift and Check.swift (line/function/region, via llvm-cov)

Validation

• swift test
• swift test --enable-code-coverage
• xcrun llvm-cov report .build/arm64-apple-macosx/debug/XCERequirementPackageTests.xctest/Contents/MacOS/XCERequirementPackageTests -instr-profile .build/arm64-apple-macosx/debug/codecov/default.profdata Sources/Core/Requirement.swift Sources/Core/Check.swift Sources/Core/Aliases.swift

Commits

• test: enforce expected throws in failure-path cases
• test: replace force-cast with safe input assertion
• docs: align Swift version metadata and install guidance
• Revert "api: make isValid rethrow evaluation errors"
• test: add coverage for requirement and nonEmpty edge paths