refactor(utxo): remove hardcoded CoinVariant in favor of ChainVariant config

[shamardy]

Summary

Refactors CoinVariant to ChainVariant, removing hardcoded ticker-based logic for block header deserialization. This logic is now explicitly defined in the coin configuration.

Configuration Changes

The coins config file must be updated. Add "chain_variant": "<VARIANT>" inside the "protocol" object for the coins listed below.

Default Behavior: If omitted, it defaults to Standard (used by KMD, LTC, DOGE, DASH, ZEC, etc.), so those coins do not require changes.

Required Updates:

Affected Coins	Chain Variant Value
BTC, BCH, NAV, RIC	"BTC"
QTUM, RUNES	"QTUM"
LBC	"LBC"
PPC	"PPC"
RICK, DOC	"RICK"
MORTY, MARTY	"MORTY"
RVN, AIPG, XNA, EVR, MEWC, AVN	"RVN"
PIVX, DOGEC	"PIVX"

Example Config:

"protocol": {
  "type": "UTXO",
  "chain_variant": "BTC" 
}

[cipig]

thanks a lot, works fine
fixes #2620