Fix wait_agent expectations in core tests

[charley-oai]

Summary

• update stale core tool-spec expectations from wait to wait_agent
• update the prompt-caching tool-name assertion to match the renamed tool
• fix the Bazel regressions introduced after Rename multi-agent wait tool to wait_agent #14631 renamed the multi-agent wait tool

Testing

• cargo test -p codex-core tools::spec::tests
• cargo test -p codex-core suite::prompt_caching::prompt_tools_are_consistent_across_requests