fix: Claude w/bedrock custom inference profile - caching support

[stevoland]

What does this PR do?

Resolves: #9803

Fixes missing cachePoint when using claude with custom inference profile, eg:

"amazon-bedrock": {
  "options": {
    "profile": "xxx",
    "region": "yyy"
  },
  "models": {
    "claude-sonnet-4.5": {
      "id": "arn:aws:bedrock:yyy:zzz:application-inference-profile/nnn"
    }
  }
},

How did you verify your code works?

./packages/opencode/script/build.ts --single

with the above config and logged tokens:

tokens: {
    input: 339,
    output: 13,
    reasoning: 0,
    cache: {
      write: 0,
      read: 19050,
    },
  },

Added failing unit test then green with the change.

TY!