feat: add `esplora_d036fb8f` electrs variant

[LagginTimes]

Description

Introduce a second Esplora‐forked Electrs binary, pinned to commit d036fb8f327d6676f3160da1ec140a4f8aee8940.

This enables array-based batching that is required by @evanlinjin's upcoming electrum_streaming_client, which may eventually replace electrum-client.

Changelog notice

• Add esplora_d036fb8f feature flag pointing at PR-108 commit d036fb8f327d6676f3160da1ec140a4f8aee8940
• Update Cargo.toml, src/versions.rs, and cfg!(feature=…) guards for the new flag
• Expand CI matrix to test both Esplora variants and add checksum placeholders for their binaries

References

Blockstream electrs PR #108 (d036fb8f327d6676f3160da1ec140a4f8aee8940)