fix: populate default values for contract_metadata

[mitinarseny]

Add #[darling(default)] attribute for link and version to make it possible to derive them from env:

#[near(contract_metadata(standard(standard = "nep141", version = "1.0.0")))
struct Contract {}

As current implementation returns an error:

error: expected an expression
 │   --> src/lib.rs:49:1
 │    |
 │ 49 | / #[near(
 │ 50 | |     contract_state,
 │ 51 | |     contract_metadata(standard(standard = "nep141", version = "1.0.0"))
 │ 52 | | )]
 │    | |__^
 │    |
 │    = note: this error originates in the attribute macro `near` (in Nightly builds, run with -Z macro-backtrace for more info)
 │ 
 │ error[E0425]: cannot find value `CONTRACT_SOURCE_METADATA` in this scope
 │   -->src/lib.rs:49:1
 │    |
 │ 49 | / #[near(
 │ 50 | |     contract_state,
 │ 51 | |     contract_metadata(standard(standard = "nep141", version = "1.0.0"))
 │ 52 | | )]
 │    | |__^ not found in this scope
 │    |
 │    = note: this error originates in the attribute macro `::near_sdk::near_bindgen` (in Nightly builds, run with -Z macro-backtrace for more info)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.07%. Comparing base (110a99a) to head (c335cf9).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1249   +/-   ##
=======================================
  Coverage   80.07%   80.07%           
=======================================
  Files         102      102           
  Lines       14598    14598           
=======================================
  Hits        11690    11690           
  Misses       2908     2908           

☔ View full report in Codecov by Sentry.
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[dj8yfo]

/compare

[github-actions]

Contract size report

Sizes are given in bytes.

contract	master	this branch	difference
adder.wasm	71721	71721	+0%
approval_receiver.wasm	89921	89921	+0%
callback_results.wasm	80722	80722	+0%
cross_contract_high_level.wasm	75382	75382	+0%
cross_contract_low_level.wasm	72282	72282	+0%
defi.wasm	94072	94072	+0%
factory_contract_high_level.wasm	169687	169687	+0%
factory_contract_low_level.wasm	167596	167596	+0%
fungible_token.wasm	162187	162187	+0%
lockable_fungible_token.wasm	110405	110405	+0%
mission_control.wasm	109843	109843	+0%
non_fungible_token.wasm	220419	220419	+0%
status_message.wasm	85472	85472	+0%
test_contract.wasm	22991	22991	+0%
token_receiver.wasm	89917	89917	+0%
versioned.wasm	93860	93860	+0%

[akorchyn]

Hey, first of all, thanks for the contribution.

Please provide example to see how it helps. It would be nice to have a test repo with test contract to make review faster