This PR is a continuation of the work done in #276
- Fix PodType in MainPod (we were using `MockMain` instead of `Main`)
- Update anchored keys in statement template arguments to only support wildcards in the origin and literal keys as the key.
- Update the pest grammar accordingly
- Update the parser accordingly
- Rewrite the eth_dos example in a recursive manner so that we use one recursive pod for every distance increment of 1.
- I've also used the podlang to define the eth_dos custom predicates. Currently all predicates are in a single batch (previously `eth_friend` was in a different batch). With #286 we could define `eth_friend` in a different batch again.
- I was feeling a bit creative and used a format macro to pass `Value`s from rust to the podlang code.
- The eth_dos is now written using literals. This resolves https://github.com/0xPARC/pod2/issues/255
- Remove `StatementArg::WildcardValue` in favor of `StatementArg::Literal`. The `WildcardValue` was just a way to have some kind of typing for values that would be used as arguments in custom predicates. Now that we can have literals in any statement this value can be anything, so I just removed the `WildcardValue` and use `Literal` instead. On the backend it was already the case that both cases were treated the same way (after all, `WildcardValue` and `Literal` were 4 fields in the backend).
- Added a new type for Value: `PodId` so that we can use it for custom predicates that take a pod id to be used in a wildcard
- Add a mock vd_set that is empty for tests that don't use plonky2; this allows running those tests individually without paying for the expensive work of calculating the vd for various circuits.
- rename StatementTmplArg::WildcardValue to StatementTmplArg::Wildcard
* Basic 'use' syntax for importing custom predicates
* Add extra test for unknown batches
* Fix unused import
* Enforce that imports must match number of predicates in a batch
* containers: add method to create new {Dict,Set,Array} with custom max_depth
* add vds_tree computation, update tree circuit interface
* add VDTree struct, add DEFAULT_VD_TREE, integrate it with MainPod,EmptyPod,frontend,etc.
* adapt frontend/serialization tests to new containers field (max_depth)
* adapt interfaces to allow using custom vd_tree in frontend & backend constructors
* rename VDTree to VDSet (and derivate namings too)
* containers 'new' always with param 'max_depth', use params.max_depth_mt_containers instead of the global constant MAX_DEPTH
* adapt after rebasing the branch to main latest changes
* apply review suggestions from @ed255
* use emptypod vd_mt_proofs (using vd_set as circuit input), merge the two existing set_targets methods of MainPodVerifyTarget
* document VDSet & vds_root
* Initial commit for Podlog language
* Spell-checker thinks that 'lits' is a bad abbreviation for 'literals'
* Enable SetContains/SetNotContains
* Update language based on review feedback
* Typo/comment fix
* Make native predicates case-sensitive
* Enforce max batch size in CustomPredicateBatchBuilder
* Remove some unnecessary checks for things handled by the grammar
* Clean up more unnecessary error-checking
* Typo
* Simplify hex processing
* Replace various errors with unreachable!()
* Translate from big-endian hex string to little-endian RawValue
* Update hex en/decoding functions
