feat(erc721): add pausable as an independent extension

[qalisander]

Current implementation of pausable doesn't need to use selectors with same ID (non unique selectors are expected to banned in future stylus sdk release).
Also there is a less possibility for user to make mistake overriding erc721 transfer-like functions.
The drawback is an additional code duplication from erc721 contract.

PR Checklist

• Tests
• Documentation

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[codecov]

Codecov Report

Attention: Patch coverage is 52.04082% with 141 lines in your changes missing coverage. Please review.

Project coverage is 82.5%. Comparing base (111b166) to head (c7da5dd).
Report is 58 commits behind head on main.

Files with missing lines	Patch %	Lines
contracts/src/token/erc721/extensions/pausable.rs	53.5%	132 Missing ⚠️
contracts/src/token/erc721/mod.rs	0.0%	3 Missing ⚠️
contracts/src/utils/pausable.rs	25.0%	3 Missing ⚠️
contracts/src/utils/structs/checkpoints.rs	0.0%	3 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
...ntracts/src/token/erc721/extensions/consecutive.rs	65.1% <ø> (+0.7%)	⬆️
contracts/src/token/erc721/mod.rs	95.7% <0.0%> (-0.3%)	⬇️
contracts/src/utils/pausable.rs	80.6% <25.0%> (-2.1%)	⬇️
contracts/src/utils/structs/checkpoints.rs	96.5% <0.0%> (-1.1%)	⬇️
contracts/src/token/erc721/extensions/pausable.rs	53.5% <53.5%> (ø)