chore: add SwiftLint and SwiftFormat configuration

[beshkenadze]

Summary

• Adds .swiftlint.yml (SwiftLint 0.63+) for static analysis
• Adds .swiftformat (SwiftFormat 0.60+) for automatic code formatting
• Adds a Code Quality section to README with setup and usage instructions

Configuration highlights

Both configs target Swift 6 and are tuned for an ML audio library. Every non-default value is annotated with a reason inline.

SwiftLint

Setting	Default → Value	Reason
file_length.warning	400 → 500	MLX model files are inherently large
function_body_length.warning/error	40/100 → 60/150	DSP routines (STFT, mel spectrogram) can't always be split further
type_body_length.warning/error	250/350 → 400/800	Model classes declare all weights as stored properties
cyclomatic_complexity.ignores_case_statements	false → true	switch over token/language IDs inflates the metric
force_cast / force_try	error → warning	Gradual adoption path; CI stays green
trailing_comma disabled	—	SwiftFormat owns trailing commas; avoids duplicate diagnostics
opt-in: force_unwrapping	off → warning	Public library safety signal
opt-in: async_without_await, unowned_variable_capture	off → on	Critical for Swift 6 strict concurrency

SwiftFormat

Setting	Default → Value	Reason
--swiftversion 6.2	none	Matches swift-tools-version; enables Swift 6 redundancy rules
--maxwidth 120	none	Consistent with SwiftLint line_length.warning
--wrap auto	preserve	Makes --maxwidth actually reformat long lines
--wraparguments/parameters/collections before-first	preserve	Readability for MLX initialisers with many named params
--guardelse next-line	auto	Async guard chains are easier to read with body on next line
--importgrouping testable-bottom	none	@testable import visually separated from production imports
--enable acronyms	off	Id → ID, Url → URL per Apple naming guidelines
--enable preferFinalClasses	off	All MLX model types are final; helps the compiler devirtualise
--enable isEmpty	off	.count == 0 → .isEmpty
--enable wrapConditionalBodies	off	Prevents easy-to-miss single-line guard else { return }

Test plan

• brew install swiftlint swiftformat locally
• swiftformat . --lint — no formatting violations on current codebase
• swiftlint lint — review any new warnings, assess if thresholds need further tuning

[beshkenadze]

Superseded by a clean branch based on upstream/main.