fix: create logs dir before writing llm request log

[J-Palomino]

Summary

RequestLog::start opened <state>/logs/llm_request.<uuid>.jsonl with File::create, which creates the file but not its parent directory. On fresh installs (or when the logs/ directory was cleared), every provider streaming request failed with ENOENT, and the providers::ollama::tests::test_stream_ollama_timeout_on_stall test panicked at the RequestLog::start(...).unwrap() call.

This change calls fs_err::create_dir_all on the logs directory at the top of RequestLog::start so the rename in finish() and the file write here both have a guaranteed parent. The existing workaround in crates/goose-acp/tests/fixtures/mod.rs (which pre-creates the dir before tests run) is no longer load-bearing.

Testing

• Added providers::utils::tests::test_request_log_start_creates_logs_dir — points GOOSE_PATH_ROOT at a fresh tempdir, asserts logs/ does not exist, calls RequestLog::start, asserts it now exists. Uses the same env_lock pattern as providers::init::tests.
• cargo test -p goose --lib providers::utils::tests::test_request_log_start_creates_logs_dir -- --exact — passes.
• cargo fmt --check -p goose — clean.
• cargo clippy -p goose --lib --tests -- -D warnings — clean.

Related Issues

Fixes #8485