[codex] apply Anthropic cache control to tools (0xPlaygrounds#1815)

* feat(anthropic): add cache_control field to ToolDefinition

Anthropic's prompt-caching API supports up to 4 cache breakpoints per
request. One of the three cacheable layers is the tools array: setting
cache_control on the last ToolDefinition tells Anthropic to cache all
tools up to that point independently of the system prompt.

ToolDefinition currently has no cache_control field, so callers have no
way to cache the tools layer. This adds the field following the same
pattern already used by SystemContent and the message Content variants.

- Add `pub cache_control: Option<CacheControl>` to `ToolDefinition`
  with `#[serde(skip_serializing_if = "Option::is_none")]` so it is
  absent from requests that do not use caching.
- Initialize `cache_control: None` at the two ToolDefinition
  construction sites (completion.rs and streaming.rs TryFrom impls).

* feat(anthropic): apply cache control to tools

* fix(anthropic): skip deferred tool cache markers

* fix(anthropic): avoid tool cache indexing

* fix(anthropic): preserve explicit tool cache markers

* fix(anthropic): budget prompt cache markers

* fix(anthropic): enforce cache marker budget

* fix(anthropic): validate cache control markers

* test(anthropic): record prompt caching cassettes

* fix(anthropic): normalize top-level cache control

* test(anthropic): cover raw cache control ttl planning

* test(anthropic): tolerate prompt cache hits on record

* docs(anthropic): refresh cache ttl docs

* test(anthropic): canonicalize streaming cache cassette

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Co-authored-by: Jimmie Fulton <jimmie.fulton@gmail.com>

Author: gold-silver-copper