Git.fetch / Git.pull: depth typed as str, inconsistent with Git.clone (int)

[tony]

Summary

depth is typed inconsistently across the git command wrappers. Git.clone and Git.submodule.update take depth: int | None and render str(depth), but Git.fetch and Git.pull take depth: str | None and pass the value straight into the argv:

# clone (L369): str() applied
local_flags.extend(["--depth", str(depth)])

# fetch (L505) / pull (L996): raw value, requires a str
local_flags.extend(["--depth", depth])

So git.clone(depth=2) works while git.fetch(depth=2) is a type error (and would place a non-str in the argv list at runtime). Callers must remember to pass "2" to fetch/pull but 2 to clone.

Suggested fix

Type depth: int | None on Git.fetch and Git.pull to match Git.clone, rendering str(depth) at the call site. --deepen could be reviewed for the same treatment.

Relevant to #532, where update_repo() would forward a numeric depth into fetch.

Acceptance

• Git.fetch(depth=2) and Git.pull(depth=2) accept an int and emit --depth 2.
• mypy passes with the unified int signature.