fix: correct bitwise-eqv to return integer instead of boolean

[aadiexii]

What is the issue?
Fixes #90

The current implementation of bitwise-eqv in srfi-151.scm
returns a boolean (#t or #f) instead of an integer, which
is incorrect according to the SRFI 151 standard.

What was changed?

• goldfish/srfi/srfi-151.scm

Before:
(define (bitwise-eqv a b)
(= (bitwise-xor a b) 0))

After:
(define (bitwise-eqv a b)
(bitwise-not (bitwise-xor a b)))

Why?
SRFI 151 specifies that bitwise-eqv should return an integer
(bitwise XNOR), not a boolean equality check.

[da-liii]

please update https://github.com/MoganLab/goldfish/blob/main/tests/goldfish/liii/bitwise-test.scm accordingly

[aadiexii]

@da-liii I have updated the tests. Lemme know if there is anything else changes or updation needed.

[da-liii]

LGTM