refactor(nfts): mapping with ApprovalsOf in the Allowances storage item

[chungquantin]

Refactoring the Allowances storage item to map the key as (collection, owner) with ApprovalsOf<T, I> as value. This change will reuse an existing ApprovalOf struct to provide the expiration feature for the collection approvals.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.62678% with 68 lines in your changes missing coverage. Please review.

Please upload report for BASE (chungquantin/feat-nfts@e8c5685). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pallets/nfts/src/weights.rs	14.06%	55 Missing ⚠️
pallets/nfts/src/features/approvals.rs	92.85%	3 Missing and 4 partials ⚠️
pallets/nfts/src/benchmarking.rs	85.00%	1 Missing and 2 partials ⚠️
pallets/nfts/src/lib.rs	84.21%	3 Missing ⚠️

@@                    Coverage Diff                    @@
##             chungquantin/feat-nfts     #390   +/-   ##
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  Coverage                          ?   70.00%           
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  Files                             ?       69           
  Lines                             ?    12388           
  Branches                          ?    12388           
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  Hits                              ?     8672           
  Misses                            ?     3452           
  Partials                          ?      264           

Files with missing lines	Coverage Δ
pallets/nfts/src/common_functions.rs	71.42% <ø> (ø)
...lets/nfts/src/features/create_delete_collection.rs	84.70% <100.00%> (ø)
pallets/nfts/src/features/transfer.rs	85.51% <100.00%> (ø)
pallets/nfts/src/tests.rs	99.89% <100.00%> (ø)
pallets/nfts/src/types.rs	67.11% <ø> (ø)
pallets/nfts/src/benchmarking.rs	85.71% <85.00%> (ø)
pallets/nfts/src/lib.rs	72.67% <84.21%> (ø)
pallets/nfts/src/features/approvals.rs	92.62% <92.85%> (ø)
pallets/nfts/src/weights.rs	2.10% <14.06%> (ø)