remove culprit

[carlsverre]

Part of a push in Graft: orbitinghail/graft#262

[Copilot]

Pull request overview

This PR removes the culprit dependency from the codebase as part of a larger effort tracked in issue #262. The changes convert all error handling from culprit::Result with context tracking to standard Rust Result types.

Key changes:

• Removed culprit dependency from Cargo.toml and Cargo.lock
• Converted all function signatures from culprit::Result<T, E> to Result<T, E>
• Simplified error construction from Culprit::new(err) to direct error returns
• Removed culprit-specific method calls like .or_into_ctx() and .ctx()
• Updated assert_error! macro to work with standard Result types
• Updated documentation examples to reflect the new error handling

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Cargo.toml	Removed culprit = "0.4" dependency
Cargo.lock	Removed culprit and smallvec (transitive dependency) package entries
src/testutil.rs	Updated assert_error! macro to not call .ctx() on errors
src/splinter_ref.rs	Converted public API from_bytes to return Result<Self, DecodeErr>, removed Culprit wrapper usage and import, updated doc example
src/cow.rs	Converted public API from_bytes to return Result<Self, DecodeErr>, removed Culprit import
src/codec.rs	Converted ensure_bytes_available to return standard Result, removed direct error wrapping with Culprit::new(), removed Culprit import
src/codec/tree_ref.rs	Converted from_suffix to return standard Result
src/codec/runs_ref.rs	Converted from_suffix to return standard Result, removed .or_into_ctx() call and ResultExt import
src/codec/partition_ref.rs	Converted all function signatures to standard Result, removed .or_into_ctx() calls and ResultExt import, cleaned up function formatting

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