fix: wrap float() in timeout_check with try/except for clean argparse error

[imxde-code]

Summary

Fixes #2866

Passing a non-numeric value to --timeout (e.g. sherlock --timeout abc user) currently raises a raw ValueError from float(value) before argparse can intercept it, producing an ugly unformatted traceback.

Root cause

# Before — raw ValueError escapes argparse
def timeout_check(value):
    float_value = float(value)   # raises ValueError for non-numeric input
    if float_value <= 0:
        raise ArgumentTypeError(...)
    return float_value

Fix

# After — non-numeric input caught and re-raised as ArgumentTypeError
def timeout_check(value):
    try:
        float_value = float(value)
    except ValueError:
        raise ArgumentTypeError(
            f"Invalid timeout value: {value}. Timeout must be a positive number."
        )
    if float_value <= 0:
        raise ArgumentTypeError(
            f"Invalid timeout value: {value}. Timeout must be a positive number."
        )
    return float_value

Argparse then formats this consistently as:

error: argument --timeout: invalid timeout_check value: 'abc'

Tests added

Two parametrized regression tests in test_ux.py:

• test_invalid_timeout_raises_argparse_error — covers non-numeric strings (abc, xyz, 1.2.3, None)
• test_non_positive_timeout_raises_argparse_error — covers zero and negative values (pre-existing bug, now also tested)

Test plan

• sherlock --timeout abc user → clean argparse error message
• sherlock --timeout -1 user → clean argparse error message
• sherlock --timeout 5 user → works normally
• New tests pass