fix(fetchers): enforce twitter fetch hardening limits

[chaliy]

Motivation

• Close a hardening bypass where TwitterFetcher followed upstream redirects and buffered API responses without honoring FetchOptions limits, which could enable SSRF or large-body exhaustion for Twitter/X syndication and oEmbed responses.

Description

• Disable automatic redirect following for the Twitter-specific client by using reqwest::redirect::Policy::none() to avoid unvalidated redirect hops.
• Enforce configured body-size and timeout limits by replacing response.text() / response.json() with the shared streaming helper read_body_with_timeout(response, BODY_TIMEOUT, max_size) and fall back to DEFAULT_MAX_BODY_SIZE when options.max_body_size is unset.
• Parse syndication JSON via serde_json::from_str on the bounded buffer (converted to UTF-8 lossily) and parse oEmbed via serde_json::from_slice on the bounded bytes, and add the use import for the helper symbols.

Testing

• Ran formatter with cargo fmt --all which completed successfully.
• Ran the targeted Rust unit tests with cargo test -p fetchkit twitter::tests -- --nocapture and the twitter fetcher tests all passed (20 passed, 0 failed).

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Codex Task