[ci] Fix cargo-deny config for v2 compatibility

[copyleftdev]

Problem

CI is failing on the cargo-deny license check step with two errors:

1. unmaintained = "warn" in [advisories] — cargo-deny v2 changed this field to expect values from ["all", "workspace", "transitive", "none"]
2. BSL-1.1 in [licenses].allow — not a recognized SPDX identifier

Fix

1. Remove deprecated unmaintained and yanked fields from [advisories]
2. Remove BSL-1.1 from the allow list
3. Add [licenses.private] section with ignore = true to skip license checks on workspace crates

Acceptance Criteria

• cargo-deny check licenses passes
• CI passes green on develop

[copyleftdev]

Fixed in PR #96. SPDX identifier corrected to BUSL-1.1, deprecated cargo-deny fields removed. CI now passes green.