test: exhaustive COBS interop tests against corncobs, porting guide, README

- 8 new interop tests cross-validating our COBS encoder/decoder against
  corncobs (including 500 random payloads). Total: 39 tests.
- New: src/board/PORTING.md — step-by-step guide to adding a new board
- New: crates/donglora-cobs/README.md — documents design choice and testing
- Updated README with lora_bridge.py example

Cargo.lock

@@ -119,6 +119,12 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "corncobs"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b0e03e9489176ebd301922fdcd0234f6dee954cbf65311863353f20d2746a8db"
+
 [[package]]
 name = "cortex-m"
 version = "0.7.7"
@@ -359,6 +365,10 @@ dependencies = [
 [[package]]
 name = "donglora-cobs"
 version = "0.1.0"
+dependencies = [
+ "corncobs",
+ "rand",
+]
 
 [[package]]
 name = "embassy-embedded-hal"
@@ -979,6 +989,17 @@ version = "2.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1d758ba1b47b00caf47f24925c0074ecb20d6dfcffe7f6d53395c0465674841a"
 
+[[package]]
+name = "getrandom"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ff2abc00be7fca6ebc474524697ae276ad847ad0a6b3faa4bcb027e9a4614ad0"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi",
+]
+
 [[package]]
 name = "half"
 version = "2.7.1"
@@ -1046,6 +1067,12 @@ dependencies = [
  "hashbrown 0.16.1",
 ]
 
+[[package]]
+name = "libc"
+version = "0.2.183"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b5b646652bf6661599e1da8901b3b9522896f01e736bad5f723fe7a3a27f899d"
+
 [[package]]
 name = "litrs"
 version = "0.4.2"
@@ -1347,6 +1374,15 @@ version = "1.13.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c33a9471896f1c69cecef8d20cbe2f7accd12527ce60845ff44c153bb2a21b49"
 
+[[package]]
+name = "ppv-lite86"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85eae3c4ed2f50dcfe72643da4befc30deadb458a9b590d720cde2f2b1e97da9"
+dependencies = [
+ "zerocopy",
+]
+
 [[package]]
 name = "proc-macro-crate"
 version = "3.2.0"
@@ -1443,11 +1479,35 @@ version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "46b71a9d9206e8b46714c74255adcaea8b11e0350c1d8456165073c3f75fc81a"
 
+[[package]]
+name = "rand"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
+dependencies = [
+ "libc",
+ "rand_chacha",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
 [[package]]
 name = "rand_core"
 version = "0.6.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
+dependencies = [
+ "getrandom",
+]
 
 [[package]]
 name = "riscv"
@@ -1838,6 +1898,12 @@ dependencies = [
  "vcell",
 ]
 
+[[package]]
+name = "wasi"
+version = "0.11.1+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ccf3ec651a847eb01de73ccad15eb7d99f80485de043efb2f370cd654f4ea44b"
+
 [[package]]
 name = "winapi-util"
 version = "0.1.11"