Add native Solana balance and transfer support

- SolanaTransaction: hand-rolled compact-u16/legacy-Message/signed-tx
  wire-format primitives, cross-validated byte-for-byte against the
  solders Python library's own serialization of an identical System
  Program transfer message.
- SolanaApi: JSON-RPC client (getBalance/getLatestBlockhash/
  getFeeForMessage/sendTransaction) over a single POST endpoint, unlike
  Tron/Bitcoin's path-per-resource REST style.
- SolanaNativeAssetBalance: getBalance polling, same design as Bitcoin's
  mempool.space polling (no push/subscription mechanism available).
- RealSolanaTransactionService: builds a single-instruction transfer
  message, signs it raw via the existing Ed25519 signer dispatch
  (skipMessageHashing - Solana signs the message directly, no external
  hashing), broadcasts via sendTransaction. Fee is Solana's actual
  getFeeForMessage answer, not a client-side estimate.
- TransactionExecution.Solana(hash) variant; wired into AssetsModule via
  a new SolanaAssetsModule, following the Bitcoin/Tron precedent exactly.

feature-account-api/src/main/java/io/novafoundation/nova/feature_account_api/data/model/Fee.kt

@@ -88,6 +88,18 @@ class TronFee(
     override val asset: Chain.Asset
 ) : Fee
 
+/**
+ * Fee for a Solana transaction, denominated in lamports, always paid in native SOL regardless of which asset is
+ * being sent (Solana has no separate "gas token" concept, same as Tron). [amount] is `getFeeForMessage`'s
+ * authoritative, exact answer for this specific compiled message (not an estimate the way Bitcoin's vsize-based
+ * fee is) - see `RealSolanaTransactionService`.
+ */
+class SolanaFee(
+    override val amount: BigInteger,
+    override val submissionOrigin: SubmissionOrigin,
+    override val asset: Chain.Asset
+) : Fee
+
 class SubstrateFeeBase(
     override val amount: BigInteger,
     override val asset: Chain.Asset