test: consolidate integration test suites into a single test runner

Disables Cargo's automatic test target discovery (autotests = false) and gathers all 24 integration test suites under a single integration test target in tests/integration.rs.

This reduces the number of separate integration test binaries from 24 to 1 across all platforms, eliminating redundant linker invocations and peak memory pressure during cargo test while significantly improving build and test times.

Cargo.toml

@@ -4,6 +4,7 @@ version = "2026.39.0"
 edition = "2021"
 build = "build.rs"
 default-run = "OpenCADStudio"
+autotests = false
 
 [workspace]
 members = [
@@ -162,3 +163,7 @@ harness = false
 [[bench]]
 name = "command_benchmarks"
 harness = false
+
+[[test]]
+name = "integration"
+path = "tests/integration.rs"