chore(build): fix build warnings for swift 6 experimental features

[thisisabhash]

Issue #

None

Description

This PR contains changes for resolving build warnings for following experimental features introduced in Swift 6:

• SE-0337: StrictConcurrency

General Checklist

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• All integration tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• New or updated tests include Given When Then inline code documentation and are named accordingly testThing_condition_expectation()
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[Copilot]

Pull Request Overview

This PR addresses build warnings for Swift 6 experimental features by resolving strict concurrency checking issues throughout the Amplify Swift codebase.

• Adds @preconcurrency imports to suppress concurrency warnings for modules not yet fully concurrency-safe
• Changes mutable static properties to immutable (var to let) where appropriate
• Adds @unchecked Sendable conformance to classes that are inherently thread-safe but don't formally conform to Sendable

Reviewed Changes

Copilot reviewed 249 out of 249 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
AmplifyTests/CoreTests/*.swift	Added @preconcurrency imports and @unchecked Sendable conformances for test classes
AmplifyTestCommon/Models/**/*.swift	Added @preconcurrency import Amplify throughout model schema files
AmplifyPlugins/**/*.swift	Added @preconcurrency imports for Combine, Amplify, and other modules; changed static var to let
AmplifyPlugins/Auth/Sources/**/*.swift	Added @unchecked Sendable conformances and nonisolated(unsafe) for static properties
AmplifyPlugins/API/Sources/**/*.swift	Updated generic constraints to include Sendable requirements for Decodable types

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[codecov]

Codecov Report

❌ Patch coverage is 52.94118% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.79%. Comparing base (5866f82) to head (2be494b).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...gin/Sync/InitialSync/InitialSyncOrchestrator.swift	0.00%	5 Missing ⚠️
...ies/DataStore/Subscribe/MutationEvent+Schema.swift	0.00%	1 Missing ⚠️
...uthPlugin/AWSCognitoAuthPlugin+AppSyncSigner.swift	0.00%	1 Missing ⚠️
...s/AWSCognitoAuthPlugin/Environment/IDFactory.swift	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4041      +/-   ##
==========================================
- Coverage   67.80%   67.79%   -0.02%     
==========================================
  Files        1129     1129              
  Lines       52478    52482       +4     
==========================================
- Hits        35585    35578       -7     
- Misses      16893    16904      +11     

Flag	Coverage Δ
API_plugin_unit_test	70.33% <100.00%> (ø)
AWSPluginsCore	69.25% <ø> (ø)
Amplify	47.93% <66.66%> (-0.02%)	⬇️
Analytics_plugin_unit_test	85.20% <ø> (ø)
Auth_plugin_unit_test	73.63% <0.00%> (+0.03%)	⬆️
DataStore_plugin_unit_test	83.33% <0.00%> (-0.16%)	⬇️
Geo_plugin_unit_test	74.86% <ø> (ø)
Logging_plugin_unit_test	65.27% <ø> (ø)
Predictions_plugin_unit_test	34.77% <ø> (ø)
PushNotifications_plugin_unit_test	88.43% <ø> (ø)
Storage_plugin_unit_test	79.39% <ø> (ø)
unit_tests	67.79% <52.94%> (-0.02%)	⬇️

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[thisisabhash]

Integration test runs succeeded.
https://github.com/aws-amplify/amplify-swift/actions/runs/17223662150
https://github.com/aws-amplify/amplify-swift/actions/runs/17223657962