Add fenced code languages for decoding-file-structure.md

[Alberto12345678999]

No description provided.

[tangos-validator]

✅ PR validation — Passed

noverify: no source/build-data changes in this PR

_{Each changed src/*.c|*.cpp is compiled and its relocated bytes compared to the binary data on a private build box. Passing requires every changed file to reproduce the ROM byte-for-byte with correct relocation targets — this catches WRONG-DEST relocations and non-reproducing near-misses that ledger-scoped linkcheck skips.}

[andrewboudreau]

Reviewed and integrated final head cc66e6178638a4243e869183d21fd38913c463b8 as squash commit 162d1796ff405da01b39d21ad753ab40aac71acb. The change only fences existing command examples in notes/decoding-file-structure.md; I corrected the shell-wrapped Python example's fence to sh on the contributor's branch. The commands themselves are unchanged. All reported checks were green before landing, including private validation and Source review. The immediate live Source review check confirmed no reconstruction-source, header, or manifest changes against target base cbfa195f63cccea8d42fc92b376470e0cf57ee1e, live tip 0133704801d79e47e36146b077ec56125889da92. Squashed through the contributor's own PR to preserve authorship.