Improve sats numeric entry for zaps

Changelog-Changed: Add number formatting for sats entry and use selected zaps amount from picker as placeholder
Changelog-Fixed: Do not allow non-numeric characters for sats amount and fix numeric entry for other number systems for all locales

damusTests/damusTests.swift

@@ -97,9 +97,9 @@ class damusTests: XCTestCase {
     
     func testSaveDefaultZapAmount() {
         let pubkey = "test_pubkey"
-        let amt = 1000
+        let amt = 1234
         set_default_zap_amount(pubkey: pubkey, amount: amt)
-        let loaded = get_default_zap_amount(pubkey: pubkey)!
+        let loaded = get_default_zap_amount(pubkey: pubkey)
         XCTAssertEqual(loaded, amt)
     }