feat(opencode): add cache_point_ttl option for Bedrock provider

[bainos]

Issue for this PR

Closes #23106

Type of change

• New feature

What does this PR do?

Adds `cache_point_ttl` to Bedrock provider options in `opencode.json` (`5m` or `1h`).
When set, a `cachePoint` block with the configured TTL is injected after the system prompt. Cache token usage is mapped into the existing token tracking.

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "amazon-bedrock": {
      "options": {
        "setCacheKey": true,
        "cache_point_ttl": "1h"
      }
    },
  }
}

                                                                                                                                                                                               ### How did you verify your code works?

Ran sessions against Bedrock Sonnet 4.6 (global inference profile). Confirmed correct TTL value appears in `cacheDetails` of the Converse API response.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[mohammadidinani]

@bainos any ETA for this?