Add missing CLI arguments for `find` and `resolve` commands (with env var fallbacks)

[karthiknadig]

Summary

The JSONRPC server's configure request accepts several configuration options that are not available as CLI arguments on the find and resolve commands. These should be added as explicit --flags with corresponding PET_* environment variable fallbacks (using clap's env attribute).

Missing CLI arguments

CLI flag	Env var	Type	Commands
--conda-executable	PET_CONDA_EXECUTABLE	Option<PathBuf>	find
--pipenv-executable	PET_PIPENV_EXECUTABLE	Option<PathBuf>	find
--poetry-executable	PET_POETRY_EXECUTABLE	Option<PathBuf>	find
--environment-directories	PET_ENVIRONMENT_DIRECTORIES	Option<Vec<PathBuf>>	find

Implementation approach

Use clap's env attribute so the CLI flag takes precedence, with the environment variable as a fallback:

/// Path to the conda/mamba executable.
#[arg(long, env = "PET_CONDA_EXECUTABLE")]
conda_executable: Option<PathBuf>,

/// Path to the pipenv executable.
#[arg(long, env = "PET_PIPENV_EXECUTABLE")]
pipenv_executable: Option<PathBuf>,

/// Path to the poetry executable.
#[arg(long, env = "PET_POETRY_EXECUTABLE")]
poetry_executable: Option<PathBuf>,

/// Additional directories where virtual environments can be found.
#[arg(long, env = "PET_ENVIRONMENT_DIRECTORIES", value_delimiter = ',')]
environment_directories: Option<Vec<PathBuf>>,

Wire these into create_config() in crates/pet/src/lib.rs so they populate the Configuration struct the same way the JSONRPC handle_configure does.

Files to modify

• crates/pet/src/main.rs — add new args to the Find command enum variant
• crates/pet/src/lib.rs — update FindOptions and create_config() to pass the new options through to Configuration

Notes

• resolve only needs --cache-directory (already present). The tool-specific executables are only used during discovery (find).
• For list-valued env vars (e.g. PET_ENVIRONMENT_DIRECTORIES), use , as the delimiter via value_delimiter = ','.
• Consider also adding PET_CACHE_DIRECTORY and PET_SEARCH_PATHS env var fallbacks to the existing --cache-directory and search paths args for consistency.