Add core validation, generation, slicing, feature extraction, and workspace metadata

[PhysShell]

Motivation

• Provide robust, validated core musical types and helpers so higher-level components can reason about pitches, durations, tempos, and time signatures safely.
• Add deterministic phrase generation, tick-range slicing, and phrase-level feature extraction to support scheduling, analysis, and generation workflows.
• Unify workspace metadata (readme, keywords, categories) across workspace members for packaging and registry consumption.

Description

• Extend core::event with ValidationError, MIDI_7_BIT_MAX, constructors and checked operations (Pitch::new, Velocity::new, Tempo::new, TimeSignature::new, Ticks::checked_add/checked_sub), Bar::duration, Phrase::duration, and make Event::duration a const fn, plus many unit tests covering validation and aggregation.
• Add core::feature implementing phrase_features which computes counts, total duration, pitch and velocity spans and returns PhraseFeatures with tests.
• Add core::generate implementing deterministic generate_repeating_phrase, bar_duration_ticks, request/ pattern types, validation, and tests for generation edge cases.
• Add core::slice implementing TickRange, TimedEvent, timed_bar_events, timed_phrase_events, and slice_phrase_events with associated tests for slicing and absolute timing.
• Export new modules from core::lib, update package manifests (Cargo.toml files) to include readme, keywords, and categories workspace metadata and enable workspace propagation, and add a generated Cargo.lock.

Testing

• Ran unit tests for the core package with cargo test -p griff-core verifying event, feature, generate, and slice behaviors and edge cases, and all tests passed.
• Ran workspace tests with cargo test --workspace to ensure integration across members and packaging metadata changes, and the test suite completed successfully.

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Codex Task