fix: optimize packages upload memory (#39366)

Bound the memory used when parsing uploaded packages, so instances with
low memory limits survive non-standard packages.

1. Metadata files are read through a size-limited reader, archives
themselves stay unbounded so large payloads keep working
2. zstd decoding caps the window at 128 MiB, the zstd CLI default
3. RPM headers go through a first-party reader with rpmlib's size and
array count limits that allocates only what the upload contains, until
https://github.com/sassoftware/go-rpmutils/pull/44 is released. Signing
still verifies the payload digest, and its signature header matches
rpmsign's byte for byte
4. Swift and NuGet read the zip entry they size-checked, a duplicate
name could stand in for it before
5. Terraform states check `LIMIT_SIZE_TERRAFORM_STATE` before parsing,
NuGet symbol PDBs share a 256 MiB budget
6. Oversized container configs are rejected instead of stored without
metadata, invalid Vagrant boxes answer 400 instead of 500

Signed-off-by: techknowlogick <git@tklk.dev>
Co-authored-by: techknowlogick <git@tklk.dev>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <techknowlogick@gitea.com>

modules/packages/limited_reader_test.go

@@ -0,0 +1,26 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package packages
+
+import (
+	"io"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLimitedReader(t *testing.T) {
+	data, err := io.ReadAll(NewLimitedReader(strings.NewReader("abc"), 3))
+	assert.NoError(t, err)
+	assert.Equal(t, "abc", string(data))
+
+	r := NewLimitedReader(strings.NewReader("abcd"), 3)
+	data, err = io.ReadAll(r)
+	assert.ErrorIs(t, err, ErrContentTooLarge)
+	assert.Equal(t, "abc", string(data))
+	n, err := r.Read(make([]byte, 8))
+	assert.Zero(t, n)
+	assert.ErrorIs(t, err, ErrContentTooLarge)
+}