add parsing for AST using chumsky

This adds parsing via `chumsky` and some necessary changes for it to
work:

- Change `error::Span` type to use byte offset for position. Also add
the `line-index` crate to replace the `line_col` method which was
previously used with the `pest` parser.
- Replace the `PestParse` trait with the `ChumskyParse` trait and the
`ParseFromStr` implementation for it.

Author: gerau

Cargo.lock

@@ -23,8 +23,6 @@ serde = ["dep:serde", "dep:serde_json"]
 
 [dependencies]
 base64 = "0.21.2"
-pest = "2.1.3"
-pest_derive = "2.7.1"
 serde = { version = "1.0.188", features = ["derive"], optional = true }
 serde_json = { version = "1.0.105", optional = true }
 simplicity-lang = { version = "0.6.0" }
@@ -34,6 +32,7 @@ itertools = "0.13.0"
 arbitrary = { version = "1", optional = true, features = ["derive"] }
 clap = "4.5.37"
 chumsky = "0.11.2"
+line-index = "0.1.2"
 
 [target.wasm32-unknown-unknown.dependencies]
 getrandom = { version = "0.2", features = ["js"] }