feat(events): add #[event] macro and IDL event support

[bristinWild]

Adds #[event] macro and IDL event schema support, enabling spel tx decode to do full typed event decoding from transaction receipts.
Changes:

IdlEvent struct added to SpelIdl (name, discriminant, fields: Vec)
events: Vec field in SpelIdl — backward-compatible, skipped if empty
#[event(discriminant = N)] proc macro to annotate event payload structs
SpelOutput::with_events() builder that auto-drains the lez-events buffer
generate_idl_json and generate_idl_fn pick up #[event] structs alongside #[instruction] functions
All 90 existing tests passing

Usage:
rust#[event(discriminant = 1)]
pub struct InsufficientFunds {
pub requested: u128,
pub available: u128,
}
Relates to: logos-blockchain/logos-execution-zone LP-0012 event system

[bristinWild]

Rebased onto upstream/main (d24dbaa, v0.4.0). Conflicts resolved , removed the lez-events crate dependency, keeping IdlEvent and #[event] as self-contained additions to spel-framework-core and spel-framework-macros. All 225 unit tests passing, 0 failures.

[vpavlin]

Thanks @bristinWild — the schema design here is clean (additive events: Vec<IdlEvent> with skip_serializing_if, no-op #[event] marker consistent with #[account_type]). But as it stands the feature is scaffolding only and doesn't function end-to-end:

• Nothing on the branch ever collects #[event]-annotated structs into SpelIdl.events. Both constructors (SpelIdl::new, generate_idl_inner) and the test literals set events: vec![], and there's no scan in generate_idl! / #[lez_program] / the account-type collector. So #[event] is a no-op and the IDL's events array is always empty.
• The test changes are just mechanical events: vec![] additions to satisfy the new field — none assert that a program with #[event] structs actually produces populated events.

To land this I'd want:

1. Collection logic that scans #[event] structs (discriminant + fields) and populates SpelIdl.events, wired into the same paths that collect #[account_type] (spel-framework-core/src/account_types.rs / idl_gen.rs / the lez_program expansion).
2. A regression test: a source with an #[event(discriminant = N)] struct → assert the generated IDL contains the event with correct name/discriminant/fields.

Happy to help wire the collection into the account-type scanner if useful. Branch is updated onto the LEZ v0.2.0 main; holding merge until the collection + test are in.