fix(codegen): emit operator==/operator<< for unions so structs containing unions compile

[devin-ai-integration]

Fixes #92.

• generateUnionType now emits operator== and operator!= using raw byte comparison over iec_byte_size, plus a test-only operator<< fallback so generated C++ headers compile when a STRUCT contains a UNION member.
• This unblocks CODESYS SysSocket types such as SOCKADDRESS, whose sin_addr field is the INADDR union.
• Added unit-test assertions in tests/backend/type-codegen.test.ts and a new tests/st-validation/data_types/union_in_struct.st + test_union_in_struct.st end-to-end fixture that exercises a SOCKADDRESS-style struct with an embedded union.

Checklist

• Tests added or updated for the changed behavior.
• npm run typecheck and npx eslint src/ --quiet pass.
• npm test passes.
• Documentation updated (IEC_COMPLIANCE.md, CODESYS_CLAIMS_LEDGER.md, README.md, etc.) if the change affects any behavior or claim covered by those docs.

Link to Devin session: https://app.devin.ai/sessions/8240483b7529498a8a4d3181be8fbe66
Requested by: @wattzor

[devin-ai-integration]

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[devin-ai-integration]

Test report: union-in-struct codegen fix

I verified the PR end-to-end on the devin/union-struct-codegen-fix branch.

End-to-end CLI proof

The new SOCKADDRESS/INADDR fixture compiles, its generated C++ operators build, the test binary passes all assertions, and strucpp --build links a runnable REPL binary.

node dist/node/cli.js tests/st-validation/data_types/union_in_struct.st \
  --test tests/st-validation/data_types/test_union_in_struct.st

node dist/node/cli.js tests/st-validation/data_types/union_in_struct.st \
  -o /tmp/sockaddr_build/ --build

Generated operators

generated.hpp now emits operator==, operator!=, and a test-only operator<< for both the INADDR union and the SOCKADDRESS struct:

Static checks & coverage

• npm run typecheck ✅
• npm run lint ✅ (exit 0; 0 errors, 605 pre-existing warnings)
• npm test ✅ (128 files / 2343 tests passed)
• npm run test:coverage ✅ — global branches 85.22% (threshold 75%)
• npx vitest run tests/backend/type-codegen.test.ts ✅ (15/15, including the new operator assertions)

Notes

• src/backend/type-codegen.ts branch coverage is 66.2% (below 75% file-level) but the overall branch gate is still met.
• npm run lint has many pre-existing warnings; the changed file adds 4 warnings and no errors.