vendor smallvec with bincode2 support

Summary:
Vendor smallvec v1 with support for bincode v2 encoding and decoding.

This was implemented in PR servo/rust-smallvec#375 which is in release 1.15.0.

Reviewed By: RajivTS

Differential Revision: D72465918

fbshipit-source-id: 04ddf5c05de7d3a9d5dea619dca331f46a40943b

Author: markbt

thrift/lib/rust/deterministic_hash/src/tests/Cargo.toml

@@ -30,7 +30,7 @@ fbthrift = { version = "0.0.1+unstable", path = "../../.." }
 futures = { version = "0.3.30", features = ["async-await", "compat"] }
 indexmap = { version = "2.9.0", features = ["arbitrary", "rayon", "serde"] }
 ref-cast = "1.0.18"
-smallvec = { version = "1.13.2", features = ["serde", "specialization", "union"] }
+smallvec = { version = "1.15", features = ["impl_bincode", "serde", "specialization", "union"] }
 thiserror = "2"
 
 [dev-dependencies]