feat: add ignore_unknown_enum_variants

[efer-ms]

This adds an option to ignore unknown enum variants on deserialization. This allows for better forward compatibility, as decoding JSON with newer enum values no longer fails, but instead defaults the enum values (typically set to UNSPECIFIED/UNKNOWN).

Add a test feature and tests specifically around this feature.

The related issue: #92

[xnorpx]

@crepererum anything more needed for this eventually get merged?

[crepererum]

Sorry, I wasn't paying attention. Code looks good, could we extend CI to also test this feature here:

pbjson/.circleci/config.yml

Lines 123 to 145 in d067f2e

	steps:
	- checkout
	- rust_components
	- cache_restore
	- run:
	name: Cargo test
	command: cargo test --workspace
	- run:
	name: Cargo test (ignore unknown fields)
	command: cargo test --workspace --features ignore-unknown-fields
	- run:
	name: Cargo test (btree)
	command: cargo test --workspace --features btree
	- run:
	name: Cargo test (emit fields)
	command: cargo test --workspace --features emit-fields
	- run:
	name: Cargo test (use integers for enums)
	command: cargo test --workspace --features use-integers-for-enums
	- run:
	name: Cargo test (preserve proto field names)
	command: cargo test --workspace --features preserve-proto-field-names
	- cache_save

[efer-ms]

Sorry, I wasn't paying attention. Code looks good, could we extend CI to also test this feature here:

pbjson/.circleci/config.yml

Lines 123 to 145 in d067f2e

	steps:
	- checkout
	- rust_components
	- cache_restore
	- run:
	name: Cargo test
	command: cargo test --workspace
	- run:
	name: Cargo test (ignore unknown fields)
	command: cargo test --workspace --features ignore-unknown-fields
	- run:
	name: Cargo test (btree)
	command: cargo test --workspace --features btree
	- run:
	name: Cargo test (emit fields)
	command: cargo test --workspace --features emit-fields
	- run:
	name: Cargo test (use integers for enums)
	command: cargo test --workspace --features use-integers-for-enums
	- run:
	name: Cargo test (preserve proto field names)
	command: cargo test --workspace --features preserve-proto-field-names
	- cache_save

Done

[xnorpx]

@crepererum can you approve workflow and see if this is good?

[efer-ms]

@crepererum , rewrote commits to match sematic conventions (I think). So it'd need another run.

[crepererum]

Can you rebase against main again? Sorry, our CI kinda broke and I've fixed it in #149.