fix: patch deps with NAT traversal fixes (proven by Mac upload to NAT testnet)

[grumbach]

Proven by live testnet upload from Mac

3/3 uploads from macOS (31s clock skew) to a 14-node NAT testnet across 4 regions. Cold: 61s. Warm: 30-33s.

What this PR does

Adds a [patch] section to the workspace Cargo.toml pointing saorsa-core and saorsa-transport at branches with proven NAT traversal fixes:

• saorsa-core -> grumbach/fix/clock-skew-tolerance (PR fix: clock skew tolerance 30s -> 5min (proven by Mac upload to NAT testnet) saorsa-labs/saorsa-core#77)
  • Clock skew tolerance: 30s -> 5min
• saorsa-transport -> grumbach/round4-combined (PR fix(nat): 8 NAT traversal fixes proven by Mac upload to NAT testnet saorsa-labs/saorsa-transport#55)
  • 8 fixes: send_ack_timeout, dedup, reachability, relay, coordinator selection

Why a patch section

The client depends on ant-node via git (branch rc-2026.4.1), which transitively pulls saorsa-core and saorsa-transport. Cargo's [patch] overrides these transitive deps with the fix branches without modifying ant-node's Cargo.toml.

Once the fix PRs are merged into rc-2026.4.1, this patch section should be removed.

Build and test

cargo build --release --bin ant
# Then upload:
SECRET_KEY=... ./target/release/ant -b <bootstrap>:10000 --evm-network arbitrum-sepolia file upload /path/to/file