Update CHANGELOG

Author: davxy

CHANGELOG.md

@@ -1,7 +1,27 @@
-## v0.6.6 [Unreleased]
+## v0.6.6 [25-06-2025]
+
+### Changes
 
 - Codebase reorganization
 - Binary to JSON conversion scripts and utilities
+* Extended the `fetch` host call with new variants.
+* Updated numeric identifiers used in `fetch`.
+* Updated numeric identifiers for PVM errors.
+* PVM wrangled operands changed.
+* Removed the traces `000...000.bin/json` step, as it was not a valid trace step and was intended to be handled specially for genesis. Since it shared the same format as regular trace steps, it could be ambiguous or misleading. 
+* Introduced an explicit `genesis.bin` file containing the genesis state and header.
+* The *authorizer trace* field has been moved to the end of the accumulation operand encoding  (C.29)
+
+### Deviations
+
+* `fetch` host call for protocol parameters ($\omega_{10}=0$) has been implemented according to this (currently) unreleased change: https://github.com/gavofyork/graypaper/pull/414
+For the `fetch` hostcall id we're still using 18 as per GP 0.6.6. The picked change only concerns the value returned for w_10=0
+
+### Extra
+
+* Codebase reorganization
+* Binary to JSON conversion scripts and utilities
+* CI: ASN.1 verification
 
 ## v0.6.5 [02-06-2025]