feat: add Swift implementation of isspam (sisspam) with CI build and benchmark integration

- Add swift_isspam package with optimized main.swift using unsafe memory flags
- Extend CI workflow to install Swift 5.9.2 and include sisspam in build_all and benchmark
- Update Makefile with build_swift target and publish step for sisspam binary
- Add sisspam to .gitignore and README with author credit
- Enable Swift timing in bench.py alongside existing language implementations

Makefile

@@ -34,7 +34,11 @@ build_jest:
 	@echo "compiling jest_rust project"
 	cd jest_rust && cargo build --release && cp target/release/jisspam ..
 
-build_all: build build_py build_cpp build_borded_cpp build_risspam build_jest
+build_swift:
+	@echo "Compiling Swift version of isspam."
+	cd swift_isspam && swift build -c release && cp .build/release/sisspam ../
+
+build_all: build build_py build_cpp build_borded_cpp build_risspam build_jest build_swift
 
 run: run_spam wl run_not_spam
 run_risspam: run_spam_risspam run_not_spam_risspam
@@ -70,6 +74,7 @@ publish:
 	@chmod +x publish
 	@./publish isspam
 	@./publish risspam
+	@./publish sisspam
 	@rm publish
 	@rm env.py