Embeddings: Display accurate percent done; do not toast continued embeddings failure

[dominiccooney]

• Do not display "Cody Embeddings Index Complete" if there's an error from the last local embeddings indexing attempt.
• Display the local embeddings percent complete in the status bar. Previously we displayed the percent incomplete.

Test plan

See https://www.loom.com/share/869556cee0dc42e4b1694f924c9e61fd?sid=8234ac0d-c984-4def-a31f-5d474d5b294d

0. Sign in with a rate-limited token.
1. Generate an incomplete embeddings index by opening a repo without embeddings, starting chat, enabling embeddings, and let it hit the rate limit. Alternatively, kill the cody-engine process and reload VSCode.
2. The status bar should indicate an appropriate, low percentage completion.
3. Resume indexing to hit the failure again. You should not see a sparkle toast that the index is complete when indexing fails.
4. Sign in with an account which can generate embeddings and resume indexing again.
5. The index should complete and you see a sparkle toast.

[philipp-spiess]

Thank you 🤗