flake.lock: Update

Flake lock file updates:

• Updated input 'blockstream-electrs':
    'github:Blockstream/electrs/9605c54' (2026-02-26)
  → 'github:Blockstream/electrs/dfcb4fe' (2026-03-31)
• Updated input 'blockstream-electrs/crane':
    'github:ipetkov/crane/444e812' (2025-08-04)
  → 'github:ipetkov/crane/0314e36' (2026-01-24)
• Updated input 'blockstream-electrs/nixpkgs':
    'github:NixOS/nixpkgs/2631b0b' (2025-04-12)
  → 'github:NixOS/nixpkgs/c5296fd' (2026-01-23)
• Updated input 'blockstream-electrs/rust-overlay':
    'github:oxalica/rust-overlay/7c13cec' (2025-08-12)
  → 'github:oxalica/rust-overlay/e9bcd12' (2026-01-26)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/b63fe7f' (2026-03-28)
  → 'github:NixOS/nixpkgs/15c6719' (2026-03-30)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/d9f52b5' (2026-03-30)
  → 'github:oxalica/rust-overlay/962a093' (2026-03-31)

Author: github-actions[bot]