upgraded workspace to Rust 2024 edition syntax semantics and rust 1.96 toolchain

[arthurianresolve]

Upgraded to current Latest Stable Syntax and Toolchain:

• latest syntax semantics: Rust 2021 ->Rust 2024 edition
• latest rust version rust 1.96.0

Code review findings fixed

• Six vendored BAML workspace crates were still edition = "2021".
• dsrs::predict_accessor used a macro-export path pattern that Rust reports as future-incompatible.
• Two jsonish parser sites had Rust 2024 tail-expression drop-order warnings.
• 2024 match ergonomics/macro fragment changes required cleanup.

!! Pre-2021 compatibility framents !!

Two macro matchers used compatibility fragments for deliberate pre-2024 expression matching behaviour!
While expr_2021 is valid Rust 1.96 / 2024 edition syntax, I nevertheless upgraded and tested them for native Rust 2024 syntax semantics.

However, should you for backward compatibility-reasons want to retain them, the references are in:

• vendor/baml/crates/baml-ids/src/lib.rs (line 4): expr_2021 -> expr
• vendor/baml/crates/bstd/src/project_fqn.rs (line 79): expr_2021 -> expr

Validation passed on Rust 1.96.0:

• rustc 1.96.0, cargo 1.96.0
• cargo fmt --all
• cargo check --workspace --all-targets --all-features --future-incompat-report
• cargo test -p baml-ids --all-features
• cargo test --workspace --all-features --no-run
• cargo test -p bstd project_fqn --all-features -- --nocapture
• cargo test -p dspy-rs named_parameters --all-features -- --nocapture
• cargo test -p jsonish --lib --all-features markdown -- --nocapture
• cargo test -p jsonish --lib --all-features multi_json -- --nocapture
• git diff --check
• rg -n "expr_2021|pat_param|keyword_idents_2024" -g "*.rs" found nothing