Migrate the hflow CLI from argparse to typed Typer commands

[kstonekuan]

The hflow CLI has roughly 750 lines of argparse setup in src/hflow/cli.py:119, Namespace-based handlers, and manual dispatch in main:1697. Migrate it to Typer so command parameters have explicit types and command registration owns dispatch.

Scope: the installed hflow command and python -m hflow.cli. Keep library operations in their existing modules. Add Typer as a direct root dependency and update uv.lock.

Acceptance criteria:

• Replace argparse setup and Namespace-based command handlers with typed Typer commands, including nested command groups.
• Preserve existing command names, positional arguments, option aliases, defaults, repeated options, boolean flag meanings, and mutually exclusive options. Local paths and object-store URLs must keep their current semantics.
• Preserve configuration and environment precedence, stdout/stderr separation, and success/failure exit codes. Keep main(argv) -> int for existing callers, including its help and parse-error SystemExit behavior.
• Keep optional runtime/server imports deferred. Help wording and layout may change, but commands and options remain discoverable through --help, and --version still works.
• Adapt existing CLI tests to exercise the command boundary. Extend coverage only for uncovered HFlow outcomes or compatibility boundaries; parser implementation assertions can be replaced. Start with tests/test_cli.py, tests/test_runtime_cli.py, and other tests importing hflow.cli.
• Keep data formats and pipeline behavior unchanged. Limit this PR to the main CLI; example migrations are separate.

Validation, following CONTRIBUTING.md:

uv sync --locked
uv run ruff check --fix
uv run ruff format
uv run ty check
uv run pytest -q
uv run hflow --help
uv run python -m hflow.cli --help

[Sravan1011]

@kstonekuan I'll take this one

[kstonekuan]

Yours.