fix: remove Windows .exe extension from binary name

Changed BINARY_NAME from lambda.exe to lambda for Unix systems.
The .exe extension is a Windows convention and is inappropriate
for macOS/Linux builds.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Makefile

@@ -1,4 +1,4 @@
-BINARY_NAME=lambda.exe
+BINARY_NAME=lambda
 
 it:
 	@ go build -o ${BINARY_NAME} ./cmd/lambda
@@ -7,13 +7,13 @@ it:
 TEST=simple
 
 run: it
-	@ ./lambda.exe - < ./samples/$(TEST).txt > program.out
+	@ ./lambda - < ./samples/$(TEST).txt > program.out
 
 profile: it
-	@ ./lambda.exe -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
+	@ ./lambda -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
 
 explain: it
-	@ ./lambda.exe -x -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
+	@ ./lambda -x -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
 
 graph:
 	@ go tool pprof -raw -output=profile/cpu.raw profile/cpu.prof