docs(docs): Move immutable ledger design docs from the catalyst-voices repo

docs/src/architecture/08_concepts/immutable_ledger/.pages

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+title: Immutable Ledger
+arrange:
+ - ledger.md

docs/src/architecture/08_concepts/immutable_ledger/cddl/block.cddl

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+block = [
+    block_header,
+    block_data: ~encoded-cbor, ; deterministically encoded CBOR
+    validator_signature,
+]
+
+block_header = [
+    chain_id: ULID,
+    height: int,
+    timestamp: ~#6.1(uint .ge 1722470400), ; Epoch-based date/time
+    prev_block_id: hash_bytes, ; hash of the previous block
+    ?ledger_type: UUID,
+    ?purpose_id: ULID / UUID,
+    ?validator,
+    ~metadata,
+]
+
+UUID = #6.37(bytes) ; UUID type
+ULID = #6.32780(bytes) ; ULID type
+
+hash_bytes = (
+  #6.32781(bytes) \ ; Blake3 hash
+  #6.32782(bytes) \ ; Blake2b hash
+  #6.32783(bytes) ; Blake2s hash
+)
+kid = hash_bytes ; hash of the x509/c509 certificate
+
+validator = (kid / [2* kid])
+metadata = [ *any ]
+
+validator_signature = (bytes / [2* bytes])

docs/src/architecture/08_concepts/immutable_ledger/cddl/genesis_to_prev_hash.cddl

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+genesis_to_prev_hash = [
+    chain_id: ULID,
+    timestamp: ~#6.1(uint .ge 1722470400), ; Epoch-based date/time
+    ledger_type: UUID,
+    purpose_id: ULID / UUID,
+    validator,
+]
+
+UUID = #6.37(bytes) ; UUID type
+ULID = #6.32780(bytes) ; ULID type
+
+validator = (kid / [2* kid])
+kid = hash_bytes ; hash of the x509/c509 certificate
+hash_bytes = (
+  #6.32781(bytes) \ ; Blake3 hash
+  #6.32782(bytes) \ ; Blake2b hash
+  #6.32783(bytes) ; Blake2s hash
+)