As an AntTP user
I want to be able safely resolve immutable PNRs
So that the data immutable PNRs resolve to cannot be changed after it has been created 

Given immutable PNRs should not return any PNR zones with mutable addresses
When resolving a PNR record with resolve_pointer in pointer_name_resolver.rs
And iteration == 0 and pointer.target == PointerTarget::ChunkAddress
Then the resolved PNR record is immutable
And resolve_pointer should be updated to return an 'isImmutable' boolean in the result
And pointer_name_resolver.resolve() must then validate that each ResolvedRecord.address is an immutable address
And if invalid then pointer_name_resolver.resolve() must return 'None'.

Given validate_immutable_addresses function already exists in pnr_service.rs
When refactoring to make this function accessible across structs
Then move validate_immutable_addresses to /src/service/mod.rs
And split it into two (validate_immutable_addresses and validate_immutable_address) to allow individual or multiple address strings to be validated
And then update pointer_name_resolver.resolve() to call validate_immutable_address to validate addresses
And then update pnr_service.get_pnr() to call validate_immutable_address to validate addresses.

Implementation Notes

- Place any unit tests at the bottom of the same file as the associated production code
- Increment patch version of anttp package in Cargo.toml
- Create a copy of this issue description and save to /spec using the name of this issue as the filename (with lower underscore case, starting with the 5 char padded issue number, e.g. 00001_issue_title.txt)
- Update unit tests to validate the changes