fix: capture commented imports in Tool requirements

[nolanchic]

What does this PR do?

Closes #2211.

get_imports() extracted imported modules with a regex anchored at end-of-line (^\s*import\s+(\S+?)(?:\s+as\s+\S+)?\s*$). Any import carrying a trailing comment failed to match, so it was silently dropped — e.g. import IPython # noqa: F401 or import numpy as np # type: ignore. As a result Tool.save / Tool.to_dict produced an incomplete requirements.txt and saved tools could be missing dependencies.

How

Rewrite get_imports to parse the snippet with ast and walk the statements. Comments are ignored by construction, and multi-name imports (import a, b) are handled correctly. textwrap.dedent is applied first so indented snippets (e.g. a tool body) parse without an IndentationError.

The previous filtering behaviour is preserved:

• imports inside try/except blocks (optional dependencies) are skipped,
• imports inside if is_flash_attn_*_available() guards (cpu-only environments) are skipped,
• relative imports (from . import x) are excluded.

Test

• Added a parametrized case to test_get_imports covering import / import ... as / from ... import each followed by an inline comment. Fails on main, passes with this change.
• All existing parametrized cases (try/except, flash-attn guard, relative imports, multi-line, import os.path) still pass.
• End-to-end: a @tool whose forward contains a commented import now lists it in to_dict()["requirements"].