apacheGH-41697: [Go][Parquet] Release BufferWriter when BufferedPageWriter is closed (apache#41698)

<!--
Thanks for opening a pull request!
If this is your first pull request you can find detailed information on
how
to contribute here:
* [New Contributor's
Guide](https://arrow.apache.org/docs/dev/developers/guide/step_by_step/pr_lifecycle.html#reviews-and-merge-of-the-pull-request)
* [Contributing
Overview](https://arrow.apache.org/docs/dev/developers/overview.html)


If this is not a [minor
PR](https://github.com/apache/arrow/blob/main/CONTRIBUTING.md#Minor-Fixes).
Could you open an issue for this pull request on GitHub?
https://github.com/apache/arrow/issues/new/choose

Opening GitHub issues ahead of time contributes to the
[Openness](http://theapacheway.com/open/#:~:text=Openness%20allows%20new%20users%20the,must%20happen%20in%20the%20open.)
of the Apache Arrow project.

Then could you also rename the pull request title in the following
format?

    GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

or

    MINOR: [${COMPONENT}] ${SUMMARY}

In the case of PARQUET issues on JIRA the title also supports:

    PARQUET-${JIRA_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

-->

### Rationale for this change

A small buffer gets reallocated after calling `Finish()`, causing that
memory to leak.

<!--
Why are you proposing this change? If this is already explained clearly
in the issue then this section is not needed.
Explaining clearly why changes are proposed helps reviewers understand
your changes and offer better suggestions for fixes.
-->

### What changes are included in this PR?
Release the buffer when the pagewriter is closed.

<!--
There is no need to duplicate the description in the issue here but it
is sometimes worth providing a summary of the individual changes in this
PR.
-->

### Are these changes tested?
Yes

<!--
We typically require tests for all PRs in order to:
1. Prevent the code from being accidentally broken by subsequent changes
2. Serve as another way to document the expected behavior of the code

If tests are not included in your PR, please explain why (for example,
are they covered by existing tests)?
-->

### Are there any user-facing changes?
Memory will not leak on this code path.

<!--
If there are user-facing changes then we may require documentation to be
updated before approving the PR.
-->

<!--
If there are any breaking changes to public APIs, please uncomment the
line below and explain which changes are breaking.
-->
<!-- **This PR includes breaking changes to public APIs.** -->

<!--
Please uncomment the line below (and provide explanation) if the changes
fix either (a) a security vulnerability, (b) a bug that caused incorrect
or invalid data to be produced, or (c) a bug that causes a crash (even
when the API contract is upheld). We use this to highlight fixes to
issues that may affect users without their knowledge. For this reason,
fixing bugs that cause errors don't count, since those are usually
obvious.
-->
<!-- **This PR contains a "Critical Fix".** -->
* GitHub Issue: apache#41697

Author: joellubi

go/parquet/internal/encoding/types.go

@@ -361,11 +361,16 @@ func (b *BufferWriter) Truncate() {
 func (b *BufferWriter) Reset(initial int) {
 	if b.buffer != nil {
 		b.buffer.Release()
+	} else {
+		b.buffer = memory.NewResizableBuffer(b.mem)
 	}
 
 	b.pos = 0
 	b.offset = 0
-	b.Reserve(initial)
+
+	if initial > 0 {
+		b.Reserve(initial)
+	}
 }
 
 // Reserve ensures that there is at least enough capacity to write nbytes

go/parquet/pqarrow/file_writer_test.go

@@ -18,6 +18,7 @@ package pqarrow_test
 
 import (
 	"bytes"
+	"math"
 	"strings"
 	"testing"
 
@@ -87,3 +88,44 @@ func TestFileWriterNumRows(t *testing.T) {
 	require.NoError(t, writer.Close())
 	assert.Equal(t, 4, writer.NumRows())
 }
+
+func TestFileWriterBuffered(t *testing.T) {
+	schema := arrow.NewSchema([]arrow.Field{
+		{Name: "one", Nullable: true, Type: arrow.PrimitiveTypes.Float64},
+		{Name: "two", Nullable: true, Type: arrow.PrimitiveTypes.Float64},
+	}, nil)
+
+	data := `[
+		{"one": 1, "two": 2},
+		{"one": 1, "two": null},
+		{"one": null, "two": 2},
+		{"one": null, "two": null}
+	]`
+
+	alloc := memory.NewCheckedAllocator(memory.DefaultAllocator)
+	defer alloc.AssertSize(t, 0)
+
+	record, _, err := array.RecordFromJSON(alloc, schema, strings.NewReader(data))
+	require.NoError(t, err)
+	defer record.Release()
+
+	output := &bytes.Buffer{}
+	writer, err := pqarrow.NewFileWriter(
+		schema,
+		output,
+		parquet.NewWriterProperties(
+			parquet.WithAllocator(alloc),
+			// Ensure enough space so we can close the writer with rows still buffered
+			parquet.WithMaxRowGroupLength(math.MaxInt64),
+		),
+		pqarrow.NewArrowWriterProperties(
+			pqarrow.WithAllocator(alloc),
+		),
+	)
+	require.NoError(t, err)
+
+	require.NoError(t, writer.WriteBuffered(record))
+
+	require.NoError(t, writer.Close())
+	assert.Equal(t, 4, writer.NumRows())
+}