Add serial module — little-endian binary serialization primitives

put_u8/16/32/64 and get_u8/16/32/64 (plus signed variants) for packing
and unpacking values at explicit byte offsets in a buffer. Each value is
encoded byte-by-byte with explicit shift operations — no struct casting,
no alignment assumptions, correct on any host endianness.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

include/serial.h

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <stdint.h>
+
+/*
+ * Binary serialization primitives.
+ *
+ * All values are encoded little-endian. Fields are placed and read
+ * explicitly by position — never by casting a struct to bytes.
+ */
+
+/* -- put: write a value into a buffer at a given byte offset -- */
+
+void put_u8 (uint8_t *buf, uint32_t offset, uint8_t  value);
+void put_u16(uint8_t *buf, uint32_t offset, uint16_t value);
+void put_u32(uint8_t *buf, uint32_t offset, uint32_t value);
+void put_u64(uint8_t *buf, uint32_t offset, uint64_t value);
+void put_i8 (uint8_t *buf, uint32_t offset, int8_t   value);
+void put_i16(uint8_t *buf, uint32_t offset, int16_t  value);
+void put_i32(uint8_t *buf, uint32_t offset, int32_t  value);
+void put_i64(uint8_t *buf, uint32_t offset, int64_t  value);
+
+/* -- get: read a value from a buffer at a given byte offset -- */
+
+uint8_t  get_u8 (const uint8_t *buf, uint32_t offset);
+uint16_t get_u16(const uint8_t *buf, uint32_t offset);
+uint32_t get_u32(const uint8_t *buf, uint32_t offset);
+uint64_t get_u64(const uint8_t *buf, uint32_t offset);
+int8_t   get_i8 (const uint8_t *buf, uint32_t offset);
+int16_t  get_i16(const uint8_t *buf, uint32_t offset);
+int32_t  get_i32(const uint8_t *buf, uint32_t offset);
+int64_t  get_i64(const uint8_t *buf, uint32_t offset);