feat(sdk)!: drop the #[fai_module] alias — #[chain_module] only

No module outside this workspace was ever published against the
alias (the system has no external users yet), so the pre-rename
name goes away instead of being maintained: one attribute, no
legacy surface. All internal doc references swept; echo example
description moves to the product name. 0.3.0.

Signed-off-by: flemming-it <sf@flemming.it>

examples/echo/Cargo.lock

@@ -34,7 +34,7 @@ checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
 
 [[package]]
 name = "chain-module-sdk"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "chain-module-sdk-macros",
  "serde",
@@ -45,7 +45,7 @@ dependencies = [
 
 [[package]]
 name = "chain-module-sdk-macros"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "proc-macro2",
  "quote",