py/mpz: Make mpz_is_zero() an inline function.

It's more efficient as an inline function, and saves code size.

py/mpz.c

@@ -939,10 +939,6 @@ void mpz_set_from_bytes(mpz_t *z, bool big_endian, size_t len, const byte *buf)
     z->len = mpn_remove_trailing_zeros(z->dig, z->dig + z->len);
 }
 
-bool mpz_is_zero(const mpz_t *z) {
-    return z->len == 0;
-}
-
 #if 0
 these functions are unused
 

py/mpz.h

@@ -111,7 +111,7 @@ void mpz_set_from_float(mpz_t *z, mp_float_t src);
 size_t mpz_set_from_str(mpz_t *z, const char *str, size_t len, bool neg, unsigned int base);
 void mpz_set_from_bytes(mpz_t *z, bool big_endian, size_t len, const byte *buf);
 
-bool mpz_is_zero(const mpz_t *z);
+static inline bool mpz_is_zero(const mpz_t *z) { return z->len == 0; }
 int mpz_cmp(const mpz_t *lhs, const mpz_t *rhs);
 
 void mpz_abs_inpl(mpz_t *dest, const mpz_t *z);