fix(models): correct chatMistralAI and chatCohere pricing by 1000x (#6393)

Pricing values in chatMistralAI and chatCohere were entered as $/1K tokens
instead of the $/token unit used by every other provider in this file.

All 17 Mistral models and 5 Cohere models had their input_cost and
output_cost divided by 1000 to match actual published pricing:
- open-mistral-nemo: $0.15/M tokens (was showing $150/M)
- mistral-large-latest: $2/M in, $6/M out (was showing $2000/$6000)
- command-r-plus-08-2024: $2.50/M in, $10/M out (was showing $2500/$10000)
- command-r-08-2024: $0.15/M in, $0.60/M out (was showing $150/$600)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>