fix: fix grammar errors in comments (#569)

## Summary
- Fix "A metadata about" -> "Metadata about" in `statistics_file.h`
(metadata is uncountable)
- Fix "a inclusive" -> "an inclusive" in `inclusive_metrics_evaluator.h`
- Fix "a estimated" -> "an estimated" in `gzip_internal.cc`

## Test plan
- No functional changes, comment-only fixes
- Build verified locally

Co-authored-by: shangxinli <shangxinli@users.noreply.github.com>

Author: shangxinli

src/iceberg/expression/inclusive_metrics_evaluator.h

@@ -48,7 +48,7 @@ namespace iceberg {
 
 class ICEBERG_EXPORT InclusiveMetricsEvaluator {
  public:
-  /// \brief Make a inclusive metrics evaluator
+  /// \brief Make an inclusive metrics evaluator
   ///
   /// \param expr The expression to evaluate
   /// \param schema The schema of the table

src/iceberg/statistics_file.h

@@ -31,7 +31,7 @@
 
 namespace iceberg {
 
-/// \brief A metadata about a statistics or indices blob
+/// \brief Metadata about a statistics or indices blob
 struct ICEBERG_EXPORT BlobMetadata {
   /// Type of the blob
   std::string type;

src/iceberg/util/gzip_internal.cc

@@ -61,7 +61,7 @@ class ZlibImpl {
     stream_.avail_in = static_cast<uInt>(compressed_data.size());
     stream_.next_in = reinterpret_cast<Bytef*>(const_cast<char*>(compressed_data.data()));
 
-    // TODO(xiao.dong) magic buffer, can we get a estimated size from compressed data?
+    // TODO(xiao.dong) magic buffer, can we get an estimated size from compressed data?
     std::vector<char> out_buffer(32 * 1024);
     std::string result;
     int ret = 0;