Fix bug when entering char in amount field on Send transaction screen

[rsrsaa]

User shouldn't be able to type chars in amount field

01:29:03.443 E FATAL EXCEPTION: main (Ask Gemini)
Process: org.bitcoindevkit.devkitwallet, PID: 5211
java.lang.NumberFormatException: Invalid number format: 'w'
at kotlin.text.StringsKt__StringNumberConversionsKt.numberFormatError(StringNumberConversions.kt:223)
at kotlin.text.UStringsKt.toULong(UStrings.kt:98)
at org.bitcoindevkit.devkitwallet.presentation.ui.screens.wallet.SendScreenKt$TransactionAmountInput$1$1$1$1$1$1.invoke(SendScreen.kt:356)
at org.bitcoindevkit.devkitwallet.presentation.ui.screens.wallet.SendScreenKt$TransactionAmountInput$1$1$1$1$1$1.invoke(SendScreen.kt:354)
at androidx.compose.foundation.text.BasicTextFieldKt.BasicTextField$lambda$46$lambda$45(BasicTextField.kt:769)
at androidx.compose.foundation.text.BasicTextFieldKt.$r8$lambda$Bgh-eOesGJvLJKMvu0N1cNulcK4(Unknown Source:0)
at androidx.compose.foundation.text.BasicTextFieldKt$$ExternalSyntheticLambda4.invoke(D8$$SyntheticClass:0)
at androidx.compose.foundation.text.LegacyTextFieldState.onValueChange$lambda$2(CoreTextField.kt:889)
at androidx.compose.foundation.text.LegacyTextFieldState.$r8$lambda$lnooYXkVzIXq96sQyl4NnPzdUYg(Unknown Source:0)
at androidx.compose.foundation.text.LegacyTextFieldState$$ExternalSyntheticLambda1.invoke(D8$$SyntheticClass:0)
at androidx.compose.foundation.text.TextFieldDelegate$Companion.onEditCommand$foundation_release(TextFieldDelegate.kt:293)
at androidx.compose.foundation.text.TextFieldDelegate$Companion.restartInput$lambda$4(TextFieldDelegate.kt:342)
at androidx.compose.foundation.text.TextFieldDelegate$Companion.$r8$lambda$Y_CeIuR19wa8lg3H7D0GWh2j-cc(Unknown Source:0)
at androidx.compose.foundation.text.TextFieldDelegate$Companion$$ExternalSyntheticLambda0.invoke(D8$$SyntheticClass:0)
at androidx.compose.foundation.text.input.internal.LegacyTextInputMethodRequest$createInputConnection$1.onEditCommands(LegacyPlatformTextInputServiceAdapter.android.kt:274)
at androidx.compose.foundation.text.input.internal.RecordingInputConnection.endBatchEditInternal(RecordingInputConnection.android.kt:191)
at androidx.compose.foundation.text.input.internal.RecordingInputConnection.addEditCommandWithBatch(RecordingInputConnection.android.kt:163)
at androidx.compose.foundation.text.input.internal.RecordingInputConnection.setComposingText(RecordingInputConnection.android.kt:229)
at androidx.compose.ui.text.input.NullableInputConnectionWrapperApi21.setComposingText(NullableInputConnectionWrapper.android.kt:125)
at com.android.internal.inputmethod.RemoteInputConnectionImpl.lambda$setComposingText$25$com-android-internal-inputmethod-RemoteInputConnectionImpl(RemoteInputConnectionImpl.java:724)
at com.android.internal.inputmethod.RemoteInputConnectionImpl$$ExternalSyntheticLambda19.run(Unknown Source:8)
at android.os.Handler.handleCallback(Handler.java:942)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loopOnce(Looper.java:201)
at android.os.Looper.loop(Looper.java:288)
at android.app.ActivityThread.main(ActivityThread.java:7924)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)

[thunderbiscuit]

Great little bug. Just FYI, we're mostly working on the Esplora and Kyoto variant these days, so if you're interested in making a PR for it, fix those!