fix(core): add Clone trait to the Declaration

[wwayne]

To fix the error

error[E0277]: the trait bound `Declaration: Clone` is not satisfied
  --> crates/tabby-common/src/api/event.rs:98:5
   |
86 | #[derive(Serialize, Deserialize, Debug, Clone)]
   |                                         ----- in this derive macro expansion
...
98 |     pub declarations: Option<Vec<Declaration>>,
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `Declaration`, which is required by `std::option::Option<std::vec::Vec<Declaration>>: Clone`
   |

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 54.40%. Comparing base (a372c6b) to head (a5ae2c6).
Report is 2 commits behind head on main.

Files	Patch %	Lines
crates/tabby-common/src/api/event.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1792      +/-   ##
==========================================
+ Coverage   54.29%   54.40%   +0.10%     
==========================================
  Files         117      117              
  Lines       10169    10226      +57     
==========================================
+ Hits         5521     5563      +42     
- Misses       4648     4663      +15     

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