Deprecate lib arg on contracttype/error/event

[leighmcculloch]

What

lib on contracttype/contracterror/contractevent now warns: deprecated.

Why

Nobody uses it. Undocumented, never shipped, zero on mainnet. Warn now, remove later.

Close #1952

[Copilot]

Pull request overview

Deprecates the unused lib argument across Soroban contract type, error, and event macros.

Changes:

• Emits a deprecation warning whenever lib is specified.
• Adds compile-fail coverage for all three macros.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
soroban-sdk-macros/src/lib.rs	Adds and applies the deprecation marker.
soroban-sdk-macros/src/derive_event.rs	Applies the warning to contract events.
soroban-sdk/tests/compile_fails.rs	Registers the new compile-fail test.
soroban-sdk/tests/compile_fails/contracttype_lib_deprecated.rs	Exercises all affected macros.
soroban-sdk/tests/compile_fails/contracttype_lib_deprecated.stderr	Captures expected diagnostics.