Exercise 2: Deleting the Duplicate Entirely — Possible Solution
====================================================================

THE FIX
------------------------------
validate_email_v2 is deleted entirely. Both original callers are
updated to use validate_email_v1_fixed - the one correct
implementation:

    def caller_a(email):
        return validate_email_v1_fixed(email)

    def caller_b(email):
        return validate_email_v1_fixed(email)

VERIFYING BOTH CALLERS GET THE CORRECT, FIXED BEHAVIOR
------------------------------
    caller_a("@b.com"): False (correctly rejected)
    caller_b("@b.com"): False (correctly rejected)
    caller_a("a@b.com"): True (correctly accepted)
    caller_b("a@b.com"): True (correctly accepted)

Both callers now correctly reject the invalid email (no local part)
and correctly accept the valid one - and, critically, they agree with
each other on both cases, which this chapter's own original duplicated
version could no longer guarantee once only one copy was patched.

WHY THIS IS A GENUINE FIX, NOT JUST A WORKAROUND
------------------------------
This chapter's own bug (v2 still incorrectly accepting "@b.com") wasn't
fixed by patching v2 to match v1_fixed's own logic - that would just
recreate the duplication this chapter identified as the root problem,
one bug fix away from diverging again the next time either copy
changes. Deleting v2 entirely and routing every caller through the one
remaining implementation means there is now exactly ONE place email
validation logic can be correct or incorrect - any future bug fix only
ever needs to happen once, and by construction, every caller
automatically gets it.

WHY THIS WORKS AS AN ANSWER
------------------------------
The duplicate is removed rather than separately patched, both original
callers are updated to depend on the single remaining implementation,
and both the previously-divergent case and a normal valid case are
verified to now agree correctly across every caller.