Adopt the central style - #8

Summary

• Applies the central swift-format configuration (mechanical reflow) across Sources and Tests.
• Judgment fix: renames the single-letter locals a/A to lowerA/upperA in INCITS_4_1986.CaseConversion Tests.swift (AlwaysUseLowerCamelCase residue) and cleans up a stray trailing-comma argument list in the same file's #expect(...) call. Both test-only; no semantic change.
• swiftlint --strict was already 0 residual before any judgment fixes were needed.
• No Benchmarks target/product stanzas present in Package.swift; nothing to remove there.

Test plan

• swift-format lint (central config), CI file set: 0 residual
• swiftlint --strict: 0 residual (109 advisory-only findings from institute package lint remain, no errors)
• Diff is style-only (formatting + test-local rename/cleanup, no production semantic change) — per lane doctrine, local build/test was skipped; hosted PR CI is the gate.