Fix/lnurl minSendable edge case when msats are not divisable by 1000

[piotr-iohk]

Description

• LNURL-pay/withdraw endpoints express minSendable / maxSendable (and withdraw bounds) in millisatoshis (msat), while Bitkit’s amount entry and validation are in whole sats.
• Previously we converted msats→sats using integer division (floor). This is usually fine when values are multiples of 1000, but it can understate the true minimum when the server returns non-round msat values (e.g. 100500 msat), letting the user enter 100 sats even though the server requires at least 101 sats.
• This PR fixes the conversion by rounding minimum bounds up (ceil) and keeping maximum bounds down (floor), preventing “amount too low” errors after the user already satisfied the UI minimum.
• Added unit tests that document the rounding rules and guard against regressions.
• additionally adding Boost toast ids (not related to fix)

Linked Issues/Tasks

• Fix/lnurl minSendable edge case when msats are not divisable by 1000 bitkit-android#529
• Verify lnurl amt rounding min/max edges bitkit-e2e-tests#72

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[Copilot]

Pull request overview

This PR fixes an edge case in LNURL amount conversion where millisatoshi values not divisible by 1000 could cause validation errors. The fix introduces proper ceiling/floor rounding when converting from millisatoshis to satoshis, ensuring minimum bounds are met and maximum bounds are not exceeded.

Key Changes

• Introduced LnurlAmountConversion utility enum with satsCeil and satsFloor methods for proper msat→sats conversion
• Updated LNURL pay and withdraw handlers to use the new conversion methods instead of integer division
• Added comprehensive unit tests covering rounding edge cases

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
Bitkit/Utilities/LnurlAmountConversion.swift	New utility enum providing ceiling and floor conversion methods from millisatoshis to satoshis
BitkitTests/LnurlAmountConversionTests.swift	Unit tests verifying correct rounding behavior for both exact and non-divisible msat values
Bitkit/ViewModels/AppViewModel.swift	Updated handleLnurlPayInvoice and handleLnurlWithdraw methods to use new conversion utilities instead of integer division

[pwltr]

utACK

[ovitrif]

utAck