OriginTrackedResource does not implement equals correctly

[zhoubiao188]

OriginTrackedResource.equals compares the wrapped Resource with the
OriginTrackedResource argument instead of with the argument's wrapped resource:

OriginTrackedResource other = (OriginTrackedResource) obj;
return this.resource.equals(other) && ObjectUtils.nullSafeEquals(this.origin, other.origin);

Resource implementations such as ClassPathResource and FileSystemResource do not
override equals, so this.resource.equals(other) is always false for a distinct
instance. Two wrappers around the same resource and the same origin are therefore never
considered equal:

Resource resource = new ClassPathResource("application.properties");
Origin origin = ...;
OriginTrackedResource a = OriginTrackedResource.of(resource, origin);
OriginTrackedResource b = OriginTrackedResource.of(resource, origin);
a.equals(b);                        // false, expected true
a.hashCode() == b.hashCode();       // true
Set.of(a, b).size();                // 2, expected 1

hashCode (which uses this.resource.hashCode()) already treats the two instances as
equal, so the equals/hashCode contract is broken: such wrappers cannot be
de-duplicated in a set or used as equal map keys.

The existing equalsAndHashCode test only asserted that an instance equals itself
(r1o1a.isEqualTo(r1o1a)) and never compared two distinct wrappers around the same
resource, which is why this went unnoticed. It now asserts that r1o1a is equal to
r1o1b as well. That assertion fails without the fix in this PR and passes with it.

The class already uses ObjectUtils.nullSafeEquals for the origin, so the same helper is
used for the resource for consistency.

[philwebb]

Thanks @zhoubiao188!