[Staking] Pallet enhancements

[DidacSF]

Description

This PR adds the following features to the nft-staking pallet:

• Adds target_index to the ContractClause struct
• Adds nft_staking_amount and nft_fee_amount to the Contract struct
• Adds checks for both stake and fee NFTs to check the amount of unique values in the extrinsic call of accept
• Adds ContractsMetadata storage, used to pair each contract with a string bytes of metadata.

Type of changes

• build: Changes that affect the build system or external dependencies (eg, Cargo, Docker)
• ci: Changes to CI configuration
• docs: Changes to documentation only
• feat: Changes to add a new feature
• fix: Changes to fix a bug
• refactor: Changes that do not alter functionality
• style: Changes to format the code
• test: Changes to add missing tests or correct existing tests

Checklist

• Tests for the changes have been added
• Necessary documentation is added (if appropriate)
• Formatted with cargo fmt --all
• Linted with cargo clippy --all-features --all-targets
• Tested with cargo test --workspace --all-features --all-targets

[codecov]

Codecov Report

Patch coverage: 58.62% and project coverage change: -0.18% ⚠️

Comparison is base (3188a40) 74.99% compared to head (429dc87) 74.81%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #341      +/-   ##
===========================================
- Coverage    74.99%   74.81%   -0.18%     
===========================================
  Files           33       33              
  Lines         3427     3443      +16     
===========================================
+ Hits          2570     2576       +6     
- Misses         857      867      +10     

Files Changed	Coverage Δ
pallets/ajuna-nft-staking/benchmarking/src/lib.rs	0.00% <0.00%> (ø)
pallets/ajuna-nft-staking/src/lib.rs	80.00% <50.00%> (-1.70%)	⬇️
pallets/ajuna-nft-staking/src/contracts.rs	93.54% <100.00%> (+0.44%)	⬆️

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[darkfriend77]

good, let's go