Delete dead shims: Lazy.cs and Dictionary.GetOrDefault (netstandard2.0)

[ChrisonSimtian]

Tier 2 — Cleanup. Two helpers carry no weight:

• src/Fallout.Utilities/Lazy.cs (~18 LOC) — Lazy.Create<T>(func) is just new Lazy<T>(func). Inline at call sites and delete.
• src/Fallout.Utilities/Collections/Dictionary.GetOrDefault.cs (~23 LOC) — a netstandard2.0-only GetValueOrDefault shim. Built into the BCL since .NET 5; the project no longer needs the polyfill.

⚠️ Breaking change

Lazy.Create is public surface → if removed outright, breaking-change + experimental + CHANGELOG migration note. Prefer an [Obsolete] forwarder for one cycle. The Dictionary shim is conditionally compiled and effectively dead.

Acceptance

• Lazy.Create call sites inlined; type obsoleted/removed
• Dictionary.GetOrDefault netstandard2.0 conditional removed
• CHANGELOG entry if any public removal

From dependency-consolidation audit, 2026-06-02.

[ChrisonSimtian]

Insights from a discarded prototype (old paths; map to onion structure after #359).

• Lazy.Create: inline the ~8 call sites to target-typed new(...); keep an [Obsolete] forwarder (it's public).
• WARNING — the issue premise is wrong: Dictionary.GetOrDefault is NOT dead. The project still multi-targets netstandard2.0, and the polyfill is reached cross-assembly via InternalsVisibleTo. Deleting it broke netstandard2.0 builds in LookupTable, ReflectionUtility, CompletionUtility, TeamCity, TeamCityAttribute (~6 sites).
• Fix before deleting: rewrite those sites to TryGetValue, then remove the file. Both TFMs then compile.