Deep audit fixes: consolidate macros, harden C-API bridging, fix Python version hardcoding, add CI & tests

[Copilot]

The ApplePy deep audit flagged critical and high-severity bugs across the macro implementations and CPython bridging layer: a stale duplicate macro target, hardcoded python3.13 that breaks the build on any other version, unchecked C-API return values that silently corrupt collections, force-unwraps that crash the interpreter, and zero CI/test coverage for most macros. This PR addresses the critical/high findings and several medium ones.

Macro consolidation

• Removed Sources/ApplePyMacroCore — a stale duplicate of Sources/ApplePyMacros that had drifted (different error handling) and was never referenced in Package.swift. ApplePyMacros is now the single source of truth.

Python version hardcoding

• module.modulemap hardcoded link "python3.13", breaking any install without that exact version. Switched ApplePyFFI's pkg-config module to python3-embed (correct for an embedding host process) and dropped the hardcoded link.
• ApplePyBundle plugin now probes python3, python3.13...python3.9 instead of assuming python3 is on PATH.
• Example build scripts (Examples/*/build.sh) had the same hardcoded version plus a macOS-only linker flag; fixed both and verified the examples build/run on Linux.

C-API bridging hardening

• Collections.swift: check return codes on PyList_SetItem, PyDict_SetItem, PySet_Add, PyTuple_SetItem, and *_Size() instead of ignoring failures.
• Added PyErr_Occurred() checks after PyIter_Next/PyDict_Next loops — both APIs return NULL/0 for "done" and "errored", so a real exception mid-iteration was being silently swallowed.
• Replaced force-unwrapped swiftPtr in generated _getSwiftValue and PyBridge.load/loadBox with nil-returning failure paths instead of crashing the whole interpreter on a corrupted Swift/Python pairing.
• Fixed reference leaks in PyEnumMacro-generated registration code on failure paths (e.g. baseBases/variantClass leaked when a later step failed).

Macro-time diagnostics

• @PyFunction now rejects async functions, generic functions, and inout parameters instead of silently generating broken wrappers.
• @PyClass rejects generic structs/classes.
• @PyProperty rejects computed properties.
• @PyEnum validates case names and parameter labels are valid, non-keyword Python identifiers (previously a param named e.g. class would generate syntactically invalid Python via raw string interpolation).
• @PyModule now reuses the correct METH_NOARGS/METH_VARARGS flag computed by @PyFunction per function, instead of hardcoding METH_VARARGS for every function regardless of arity.

CI and testing

• Added a swift test GitHub Actions workflow (macOS + Linux matrix) — previously only a docs-publishing workflow existed.
• Discovered assertMacroExpansion (from SwiftSyntaxMacrosTestSupport) reports failures via XCTFail, which is silently swallowed when called from Swift Testing @Test functions — every macro-expansion test was passing regardless of actual output. Switched to the framework-agnostic SwiftSyntaxMacrosGenericTestSupport API with a custom failure handler wired to Issue.record, so these tests now genuinely validate expansion. This surfaced a real bug in @PyUnion (emitting broken empty conformance extensions when misapplied to a non-enum), now fixed.
• Backfilled test coverage for Set<T>, PyTuple2, PyTuple3, bytes/bytearray conversion, and the new macro diagnostics (18 → 36 tests).

Other medium-priority fixes

• Documented the @unchecked Sendable safety invariant (GIL-serialized access) on PyObjectBox and PyExceptionType.
• BufferBridge.bytesFromPython now type-checks with PyBytes_Check/PyByteArray_Check before extracting (also adds previously-unsupported bytearray handling) and guards negative size results.
• Fixed silent Int64 → Int truncation in Primitives.swift; documented Float/Double precision loss.
• Pinned swift-syntax to 600.0.0..<700.0.0 instead of an open-ended from: range; pinned GitHub Actions by SHA.

Known gap (pre-existing, not introduced here)

@PyClass doesn't currently wire up codegen for @PyMethod instance methods, @PyProperty getters/setters, or @PyStaticMethod — these attributes validate correctly but aren't read by @PyClass's member generation. Flagging for a follow-up since it's a larger change than this audit pass.

[jagtesh]

@copilot we should add support for the latest (and upcoming) python versions.

[jagtesh]

Add the newer python versions, 3.14 and 3.15

[Copilot]

Added python3.14 and python3.15 to the probe list in e28b19b.

[Copilot]

@copilot we should add support for the latest (and upcoming) python versions.

Added python3.14 and python3.15 to the interpreter probe list in e28b19b.