Implement interpreter in Rust

[starpit]

Is your feature request related to a problem? Please describe.
Ability to run in browser, and other non-python-friendly environments. Improve startup time. Establish a common ground across the many agent libraries, by providing a common AST+interpreter+toolchain.

Describe the solution you'd like
By implementing the interpreter in Rust, we achieve many of these goals. For example, Rust has a direct path to WASM, which enables running at least partially in a serverless web app. It also allows PDL to be embedded into other python projects while avoiding python versioning issues.

Describe alternatives you've considered
We could instead have implemented a set of interpreters, e.g. one in python, one in typescript, ...

Punch List

We have already merged (via #857) some initial work on this. Remaining work is summarized below.

Orthogonal Features

• --data and --data-file command line option feat: support for --data and --data-file in rust interpreter #894
• trace generation feat: initial pdl__id and --trace support for rust interpreter #912
• defsite information for messages
• parallel model calls
• stream none feat: rust interpreter support for modelResponse, ollama-rs tooling calling, and no-stream #883
• contribute
• parser: json
• parser: jsonl fix: rust ast support for gsm8k, including jsonl parser #924
• parser: yaml
• parser: regex findall, findmatch, match, default feat: some regex parser support for rust interpreter #929
• parser: regex split mode (stubs in place, with todo!() panic
• parser: pdl (missing from ast)
• join
• python structs in PdlResult
• concrete types for LocalizedExpression instead of String feat: introduce Expr typing and apply it to IfBlock.condition #899 feat: update rust Call AST to use Expr for condition attr #901 feat: update rust Repeat AST to use Expr for for attr #904 fix: in rust ast, allow ModelBlock model to be an expr #911 fix: update rust interpreter to create Data blocks for expr eval, and model_input trace field #914
• line number information
• minijinja eval_str -> render_and_return_state and... somehow make PdlResult compatible with state.lookup() results

Blocks

• String block
• Jinja expansions
• MessageBlock
• TextBlock basic
• TextBlock def
• TextBlock defs
• ModelBlock Ollama
• ModelBlock Ollama tool calling feat: rust interpreter support for modelResponse, ollama-rs tooling calling, and no-stream #883
• ModelBlock non-Ollama
• ModelBlock granite.io
• CallBlock (no args)
• CallBlock (with args)
• CodeBlock Python
• CodeBlock Python pips
• CodeBlock Python cross-block variables
• CodeBlock other
• EmptyBlock
• IfBlock
• RepeatBlock
• MatchBlock
• DataBlock
• ArrayBlock
• ObjectBlock
• LastOfBlock
• ReadBlock stdin
• ReadBlock text file
• ReadBlock struct file with def
• ReadBlock multiline feat: add support for multiline reads to rust interpreter #868
• ImportBlock
• IncludeBlock

TO BE DEPRECATED

• GetBlock