* migrate from anyhow to thiserror (#190). pending polish error msgs
* Add backtrace and compartmentalize errors
- Include backtraces in the errors we generate. To get this we can't
just return a literal enum, because the backtrace requires a call.
- Related to the previous point: add methods to create errors so
we can include the backtrace conveniently without changing too much
the syntax. So instead of `Err(Error::KeyNotFound(key))` (literal
enum) it will be `Err(Error::key_not_found(key))` (method call)
- Each error should be local to its scope, and each scope should
only return its own error.
- The merkle tree should return `TreeError` and not Error
- The middleware should return `MiddlewareError` and not Error
- With a global Error we can't easily include backend/frontend types in
the error fields, so declare a `BackendError` and a `FrontendError`
and follow the pattern from the previous point
- The Pod traits should be able to return backend errors and will be
used in the frontend; for that we change them to use trait object
Error: `dyn std::error::Error`
* fix error
* apply suggestions from @arnaucube
* rename XError and XResult to Error and Result
* reorg signature
* make frontend custom error more ergonomic
* remove unnecessary feature
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Co-authored-by: Eduard S. <eduardsanou@posteo.net>
