fix: let unannounced channels take full-size payments

[ovitrif]

Refs:

• bug: incoming lightning payments above 10% of the channel size fail bitkit-android#1388
• bug: incoming lightning payments above 10% of the channel size fail bitkit-ios#850

Description

• Sets the maximum inbound HTLC value in flight to 100% of the channel value for nodes that cannot announce channels (no node alias or no listening addresses), so a single incoming payment can use the whole channel instead of 10% of it. Such a node only accepts unannounced channels, and ldk-node already sets 100% for the unannounced channels it opens itself.
• The limit is part of the channel handshake, so channels opened before this change keep their 10% limit; only new channels benefit.
• Adds inbound_htlc_in_flight_limit_for_unannounced_node: opens a 1,000,000 sat channel to a node without an alias, pays it 9% (works with and without the change) and 20% of the channel value (fails with PaymentSendingFailed without the change).
• Upstream rust-lightning makes 100% the default for unannounced channels (2867d5c1a, in the 0.3 pre-releases); the fork is on LDK 0.2.0, where it is still 10%.
• The changelog line goes into the release PR, per the fork's single-section CHANGELOG rule.

Out of Scope

• src/builder.rs, src/event.rs: the LSPS2 paths keep their own 100% override.
• Nodes that can announce keep LDK's default for every inbound channel, unannounced ones included; no config option is added.
• Existing channels: the limit is fixed at channel open, so they stay at 10%.
• Version bump and release: separate release PR, followed by the bump PRs in the Bitkit apps.
• Newer LDK defaults 100% for unannounced channels (unannounced_channel_max_inbound_htlc_value_in_flight_percentage); when the fork moves to an LDK release with that option, this override can be removed.

QA Notes

Automated Checks

• added inbound_htlc_in_flight_limit_for_unannounced_node in tests/integration_tests_rust.rs: failed on main (a payment above 10% of the channel value must be routable: PaymentSendingFailed), passes with the change.
• ran lsps2_client_service_integration, lsps2_client_trusts_lsp, lsps2_lsp_trusts_client_but_client_does_not_claim, multi_hop_sending: pass.
• channel_full_cycle_electrum did not finish locally: it stops at the splice step on main as well as with the change. CI here is manual (rust.yml runs on workflow_dispatch); I dispatched it on this branch (https://github.com/synonymdev/ldk-node/actions/runs/36661558748): the ubuntu stable build fails on warnings that main has too, and fail-fast cancelled the rest, so the full suite has not run yet. It is the readiness gate once main builds on stable.

Manual Tests

• Bitkit Android master (2.5.0) on a regtest LND channel of 1,000,000 sats, with a libldk_node built from 0.7.0-rc.66 plus this one-line change swapped in: the channel is accepted with max_htlc_value_in_flight_msat: 1000000000 (was 100000000), and single payments of 110,000 sats (11%) and 500,000 sats (50%) succeed with "Received Instant Bitcoin". Without the change the 11% payment fails.

[ovitrif]

Pushed 555d5db: dropped the changelog entry from this PR; the release PR adds it in the fork's single section. Dispatched the Rust CI on this branch: https://github.com/synonymdev/ldk-node/actions/runs/36661558748

[ovitrif]

The Rust CI run on this branch (https://github.com/synonymdev/ldk-node/actions/runs/36661558748) failed in "build (ubuntu-latest, stable)", and fail-fast cancelled the other jobs. The failure is on main too (26664614): with --features uniffi and -D warnings, rustc 1.98.1 rejects four unused imports in src/ffi/types.rs (lines 45, 48-50, 54, 63) and the deprecated bitcoin::FeeRate::from_sat_per_vb_unchecked used by the constructor at bindings/ldk_node.udl:416. This PR touches neither. The same build passes on 1.85.0 and on beta, so the test steps never ran; they need a run once main builds on stable.