chore: Replace positive? with 'greater than 0' (#1586)

Opentelemtry used in many projects and micro performance could impact a lot.
The default rubocop style was not designed in performance overview.

[subjective] Benchmarks shows the `Numeric#positive?` is 1.32x slower, than 'number > 0'.

```
ruby 3.3.0 (2023-12-25 revision 5124f9ac75) +YJIT [arm64-darwin23]
Warming up --------------------------------------
      compare with 0     1.000 i/100ms
           positive?     1.000 i/100ms
Calculating -------------------------------------
      compare with 0      3.153 (± 0.0%) i/s -     95.000 in  30.132600s
           positive?      2.397 (± 0.0%) i/s -     72.000 in  30.042688s

Comparison:
      compare with 0:        3.2 i/s
           positive?:        2.4 i/s - 1.32x  slower
```

The change disables Style/NumericPredicate for rubocop as well.

Signed-off-by: Michael Nikitochkin <michael.nikitochkin@gmx.net>
Co-authored-by: Kayla Reopelle (she/her) <87386821+kaylareopelle@users.noreply.github.com>
Co-authored-by: Robert <robertlaurin@users.noreply.github.com>

sdk/.rubocop.yml

@@ -20,3 +20,5 @@ Style/ExplicitBlockArgument:
   Enabled: false
 Style/ModuleFunction:
   Enabled: false
+Style/NumericPredicate:
+  Enabled: false

sdk/lib/opentelemetry/sdk/trace/export/batch_span_processor.rb

@@ -80,7 +80,7 @@ def on_finish(span)
             lock do
               reset_on_fork
               n = spans.size + 1 - max_queue_size
-              if n.positive?
+              if n > 0
                 dropped_spans = spans.shift(n)
                 report_dropped_spans(dropped_spans, reason: 'buffer-full', function: __method__.to_s)
               end