feat: initialize project structure and error types

- go.mod with github.com/dailz/go-kv, Go 1.26.3, testify
- config/config.go with WalConfig, Validate() with checked arithmetic
- errors.go with sentinel errors (ErrCommitUnknown, ErrWriteStopped, etc.)
- wal/constants.go with all WAL format constants and enums
- wal/header.go with WAL File Header encode/decode (CRC32 IEEE)
- wal/record.go with Physical Record codec, block boundary, SplitIntoRecords
- wal/entry.go with WAL Entry codec (varint keys/values, OpType, ValueKind)
- wal/sequence.go with SequenceManager (atomic, CAS, overflow-safe)
- manifest/manifest.go with MANIFEST stub (Load/Save atomic)
- manifest/current.go with CURRENT file (WriteCurrent/ReadCurrent)
- Comprehensive tests for all modules
- .golangci.yml configuration

wal/constants_test.go

@@ -0,0 +1,72 @@
+package wal
+
+import "testing"
+
+func TestConstantValues(t *testing.T) {
+	tests := []struct {
+		name     string
+		got      interface{}
+		expected interface{}
+	}{
+		{"WalBlockSize", WalBlockSize, 32 * 1024},
+		{"WalFileHeaderSize", WalFileHeaderSize, 32},
+		{"WalBatchHeaderSize", WalBatchHeaderSize, 18},
+		{"PhysicalRecordHeaderSize", PhysicalRecordHeaderSize, 7},
+		{"MaxWalBatchEntriesSize", MaxWalBatchEntriesSize, uint32(4 * 1024 * 1024)},
+		{"MaxWalBatchEntryCount", MaxWalBatchEntryCount, uint32(10000)},
+		{"MaxWalKeyBytes", MaxWalKeyBytes, uint32(4 * 1024)},
+		{"MaxWalInlineValueBytes", MaxWalInlineValueBytes, uint32(4 * 1024)},
+		{"MaxWalVarintBytes", MaxWalVarintBytes, 5},
+		{"DefaultMaxWalSegmentSize", DefaultMaxWalSegmentSize, uint64(64 * 1024 * 1024)},
+		{"WalMagic", WalMagic, uint32(0x57414C4B)},
+		{"WalFormatVersion", WalFormatVersion, uint16(1)},
+	}
+
+	for _, tt := range tests {
+		if tt.got != tt.expected {
+			t.Errorf("%s = %v, want %v", tt.name, tt.got, tt.expected)
+		}
+	}
+}
+
+func TestFragmentTypes(t *testing.T) {
+	if RecInvalid != uint8(0) {
+		t.Errorf("RecInvalid = %d, want 0", RecInvalid)
+	}
+	if RecFull != uint8(1) {
+		t.Errorf("RecFull = %d, want 1", RecFull)
+	}
+	if RecFirst != uint8(2) {
+		t.Errorf("RecFirst = %d, want 2", RecFirst)
+	}
+	if RecMiddle != uint8(3) {
+		t.Errorf("RecMiddle = %d, want 3", RecMiddle)
+	}
+	if RecLast != uint8(4) {
+		t.Errorf("RecLast = %d, want 4", RecLast)
+	}
+}
+
+func TestOpTypes(t *testing.T) {
+	if OpInvalid != uint8(0) {
+		t.Errorf("OpInvalid = %d, want 0", OpInvalid)
+	}
+	if OpPut != uint8(1) {
+		t.Errorf("OpPut = %d, want 1", OpPut)
+	}
+	if OpDelete != uint8(2) {
+		t.Errorf("OpDelete = %d, want 2", OpDelete)
+	}
+}
+
+func TestValueKinds(t *testing.T) {
+	if VKNone != uint8(0) {
+		t.Errorf("VKNone = %d, want 0", VKNone)
+	}
+	if VKInline != uint8(1) {
+		t.Errorf("VKInline = %d, want 1", VKInline)
+	}
+	if VKValueLogPointer != uint8(2) {
+		t.Errorf("VKValueLogPointer = %d, want 2", VKValueLogPointer)
+	}
+}