fix(antigravity): map model ID 1417 to gemini-4-argon - #1894

Maps Antigravity numeric model ID 1417 to gemini-4-argon in model_name_from_id (rust/adapters/antigravity/src/parser.rs), which already exists in models-dev-pricing.json, so the ~4.6M previously unpriced tokens now resolve to priced usage instead of model_placeholder_m417 with a missing-pricing warning. Also adds the model_placeholder_m417 -> gemini-4-argon entry in normalize_antigravity_model so rows recorded with the placeholder name are priced too, matching the established numeric-arm-plus-placeholder pattern. Extends the existing normalizes_newer_gemini_model_placeholders_and_ids regression test with the 1417 / placeholder / display-name case.

Tests: cargo test -p ccusage-adapter-antigravity passes (33 passed, 0 failed, including the extended placeholder test); cargo clippy -p ccusage-adapter-antigravity --all-targets is clean. IDs 1277 and 1050 from the report were left untouched since their model identities are unknown.

Changes left uncommitted in the working tree as instructed.

Closes #1893

Summary by cubic

Resolves Antigravity model ID 1417 and the related model_placeholder_m417 name to gemini-4-argon, pricing the ~4.6M tokens that previously fell through to a placeholder with a missing-pricing warning. Extends the existing regression test to cover the new mapping.

^{Written for commit a628ec6. Summary will update on new commits.}