Support multipart upload

[LeMikaelF]

I used the opportunity to also add tests for v1 upload.

AI disclosure

Claude wrote most of the code, but I revised it and iterated on it.

[Copilot]

Pull request overview

This pull request adds multipart upload support for large database files to the Turso CLI, allowing efficient uploads of files over 100MB. The implementation includes comprehensive test coverage for both single-part (v1) and multipart (v2) upload flows, with proper progress tracking and error handling.

Key changes:

• Added multipart upload implementation with automatic threshold-based selection (100MB)
• Implemented comprehensive test suite for upload functionality with mock server
• Added --multipart flag to force multipart upload mode

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
internal/turso/tursoServer_test.go	Comprehensive test suite with mock server, test helpers, and tests for single-part, multipart, and progress tracking functionality
internal/turso/tursoServer.go	Core multipart upload implementation with chunk management, progress tracking, and file locking
internal/turso/turso.go	Added PutBinary method and Content-Length header handling for chunk uploads
internal/turso/databases.go	Integrated multipart upload logic with automatic threshold-based selection (100MB)
internal/cmd/group_flag.go	Updated flag parsing functions to support multipart parameter
internal/cmd/db_create.go	Added multipart flag parameter to database creation flow
internal/cmd/db_import.go	Declared and registered --multipart flag for import command
go.mod	Added testify dependency for improved test assertions

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[LeMikaelF]

This PR is good to go, but this error in CI prevents me from merging:

⣾ Creating group t74e5er2qqazsnbufj-aws-us-east-1 at aws-us-east-1...
Error: received response with status code 400: Input error: unable to register exclusive lock on node ["93595be9-ea47-11ed-9933-bed7d3860eaa"] (deletion must be in progress)

I'm investigating ⌛