Deal with Coingecko price validator's loose JDT typing

We ended up with some implicit anys and unexpected unknowns due to the
JDT schema's inability to type a few properties. With noImplicitAny,
this triggers actual errors, and we adjust for those here.

background/lib/prices.ts

@@ -29,7 +29,11 @@ export async function getPrice(
     return null
   }
 
-  return json ? parseFloat(json[coingeckoCoinId][currencySymbol]) : null
+  return json
+    ? parseFloat(
+        json[coingeckoCoinId][currencySymbol] as string // FIXME Drop as when strict mode arrives and price schema type can include this.
+      )
+    : null
 }
 
 function multiplyByFloat(n: bigint, f: number, precision: number) {
@@ -78,7 +82,7 @@ export async function getPrices(
               amounts: [
                 multiplyByFloat(
                   BigInt(10) ** BigInt(c.decimals),
-                  parseFloat(simpleCoinPrices[symbol]),
+                  parseFloat(simpleCoinPrices[symbol] as string), // FIXME Drop as when strict mode arrives and price schema type can include this.
                   8
                 ),
                 BigInt(1),

background/lib/validation.ts

@@ -24,7 +24,7 @@ const coingeckoPriceSchema = {
     },
     additionalProperties: true,
   },
-}
+} as const
 
 type CoinGeckoPriceDataJtd = JTDDataType<typeof coingeckoPriceSchema>