feat(lazer/stellar-example): bump to soroban-sdk 26 + pyth-lazer-stellar-sdk 0.3 + wasm32v1-none

[jayantk]

Tracks the Stellar example consumer at lazer/stellar/ to the republished SDK, mirroring the canonical bump pattern from [[p-fssmjczh]]. Resolves [[i-zwfldyou]].

Changes

• Cargo.toml: pyth-lazer-stellar-sdk 0.2 → 0.3; soroban-sdk 22.0.5 → 26.1.0. The alloc feature still exists in soroban-sdk 26 (the upstream SDK crate keeps features = ["alloc"]), so it is retained.
• Cargo.lock: regenerated via cargo update -p pyth-lazer-stellar-sdk -p soroban-sdk. pyth-lazer-stellar-sdk v0.3.0 now resolves from registry+crates.io with checksum febb846686d4e4124d59e32517a3165cc34a5d04ac48557d86a706f56f0b1049.
• rust-toolchain.toml (new): pins channel = "1.91.1" with targets = ["wasm32v1-none"], mirroring pyth-lazer/contracts/stellar/rust-toolchain.toml.
• README.md: build target wasm32-unknown-unknown → wasm32v1-none (prereq, build cmd, artifact path, deploy --wasm path); notes minimum Rust 1.84. Testnet verifier id CD2KMDOR274ZVPVVSDIBWNBLGAXJOHKJBQGNWYQHF3O6H767UOYJJYJZ unchanged.
• CI (.github/workflows/ci-lazer-stellar.yml): build target switched to wasm32v1-none in setup-rust-toolchain, clippy, and build steps.

API stability

Confirmed the breaking-change inventory holds: the example uses PythLazerClient::new, verify_update, Feed.{price, exponent, feed_update_timestamp}, and instance storage — all stable across the bump. No src/ changes were needed; the crate compiles unchanged.

Verification

All checks run locally from lazer/stellar/ with the 1.91.1 toolchain, mirroring CI:

• taplo fmt --check on Cargo.toml — clean.
• cargo fmt --all -- --check — clean.
• cargo clippy --release --target wasm32v1-none --locked -- --deny warnings — clean.
• cargo build --release --target wasm32v1-none --locked — produces target/wasm32v1-none/release/pyth_lazer_stellar_example.wasm (27901 bytes).
• git merge-tree origin/main HEAD — no conflicts.