Fix logarithm mapping max scale comment and align with Go implementation

opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/exponential_histogram/mapping/logarithm_mapping.py

@@ -47,8 +47,12 @@ def _get_min_scale(self):
         return self._min_scale
 
     def _get_max_scale(self):
-        # FIXME The Go implementation uses a value of 20 here, find out the
-        # right value for this implementation, more information here:
+        # _max_scale is 20. The OpenTelemetry specification requires that
+        # bucket indices fit within a signed 32-bit integer. At scale 20,
+        # the maximum bucket index is ((MAX_NORMAL_EXPONENT + 1) << 20) - 1,
+        # which fits within this range. At scale 21, the maximum bucket
+        # index reaches the upper limit of a signed 32-bit integer, making
+        # it difficult to test correctness. See:
         # https://github.com/lightstep/otel-launcher-go/blob/c9ca8483be067a39ab306b09060446e7fda65f35/lightstep/sdk/metric/aggregator/histogram/structure/README.md#mapping-function
         # https://github.com/open-telemetry/opentelemetry-go/blob/0e6f9c29c10d6078e8131418e1d1d166c7195d61/sdk/metric/aggregator/exponential/mapping/logarithm/logarithm.go#L32-L45
         return self._max_scale