Propagate magic opt-out flags through MagicAlias - #15365

Fixes #13064

Magics created via %alias_magic don't carry the target magic's opt-out flags. run_line_magic/run_cell_magic read MAGIC_NO_VAR_EXPAND_ATTR, needs_local_scope and MAGIC_OUTPUT_CAN_BE_SILENCED off the registered object; on a MagicAlias those attributes don't exist, so {var} in an aliased call gets interpolated from user_ns before execution (the stale-i f-string symptom from the issue), and aliases of needs_local_scope magics lose access to function locals.

Give MagicAlias property delegates that resolve the aliased magic at call time — the class already documents late binding — and report the target's flags. The lookup walks alias chains iteratively and stops on cycles, so a self-referencing alias terminates and raises the original UsageError instead of recursing forever. A missing target yields False, i.e. today's behavior.

Regression tests (all in tests/test_magic.py):

• test_alias_magic_no_var_expand — line alias of %time does not expand {a}
• test_alias_magic_cell_no_var_expand — same through the cell path, %%timeit setup line
• test_alias_magic_needs_local_scope — alias sees the caller's function locals
• test_alias_magic_fstring_loop — exact repro from the issue
• test_alias_magic_flag_lookup_on_self_loop — cyclic alias terminates

Checked in a fresh sandbox on upstream main (dd41c52): the new flag tests fail without the change as expected; with it, 130 passed, 6 skipped in tests/test_magic.py.