test: harden parity coverage and bump version to 0.7.5

[rlippmann]

Summary

• add targeted TypeScript regression tests for parity gaps identified against the Python source of truth
• harden demo and example smoke oracles to prefer structural and behavioral assertions over formatting-sensitive output checks
• bump package version from 0.7.4 to 0.7.5

Why

• improve cross-language parity confidence without changing production behavior
• reduce brittle test failures caused by incidental output formatting or copy changes
• publish the test hardening work under a patch release within the existing Python-compatible 0.7.x line

Scope checklist

• Diff is minimal and scoped to the requested behavior
• Python/spec parity is preserved (or mismatch is explicitly documented)
• Fixture semantics are respected (exact string vs non-empty null rule)
• No unrelated refactors
• Relevant validation was run (npm test for behavior changes)

Notes

Validation details:

• npm test: passed
• If not run, why: n/a