Bump SurrealDB to 3.1.3

Upgrade the embedded `surrealdb` crate 3.0.5 -> 3.1.3 (latest 3.1.x) and
keep the Rust package version aligned.

- surrealdb dependency and package version -> 3.1.3
- Cargo.lock regenerated (cargo update --precise)
- rust-toolchain.toml channel 1.91 -> 1.95, aligned with the toolchain
  SurrealDB 3.1.x is built with
- CHANGELOG [Unreleased] entry added

cargo check passes on toolchain 1.95 with no changes to the JNI bindings;
the 3.1 API is source-compatible with the driver.

Author: emmanuel-keller

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## [Unreleased]
+- Upgrade to SurrealDB SDK 3.1.3 and bump the Rust toolchain to 1.95 [#165](https://github.com/surrealdb/surrealdb.java/pull/165).
 
 ## [2.0.3] - 2026-05-29
 - Support Java `record` classes in `create` and `select` (JDK 16+ at runtime). Records are hydrated via their canonical constructor; POJO behaviour on JDK 8+ is unchanged [#156](https://github.com/surrealdb/surrealdb.java/pull/156).