Add typed language foundations for 0.1.0-rc.3

[kleeedolinux]

Summary

Expand the statically typed Pop Lang foundation for 0.1.0-rc.3 and add the
roadmap toward the first supported 0.1.0 release.

This change adds:

• typed string concatenation, escapes, interpolation, and conversion;
• decimal floats, complete numeric ordering, casts, and checked conversions;
• numeric for ranges, break, and continue;
• conditional expressions and elseif;
• typed compound assignment with single-evaluation targets;
• fixed type packs, tuple projection, destructuring, and multiple returns;
• typed table lookup, insertion, replacement, and deterministic growth;
• runtime constants, erased type aliases, and nominal scalar enums;
• explicit callable generics, generic records, and generic tagged unions;
• deterministic specialization of reachable generic functions and data in MIR;
• MIR-interpreter and LLVM execution coverage for the new language features;
• fail-closed C-backend rejection where runtime capabilities are unsupported;
• ROADMAP.md covering the remaining 0.1.0 release blockers;
• release-workflow restrictions for the upstream repository.

Optional narrowing, generalized iteration, the complete typed-error workflow,
and the remaining production runtime/tooling work are intentionally tracked in
the roadmap rather than presented as completed.

Architecture traceability

• Authorizing architecture section or ADR:
  • ADR 0040: decimal float literals and numeric conversions
  • ADR 0041: typed string composition and formatting
  • ADR 0042: numeric ranges and loop control
  • ADR 0043: conditional expressions
  • ADR 0044: compound assignment
  • ADR 0045: fixed type packs and multiple assignment
  • ADR 0046: typed table access and mutation
  • ADR 0047: evaluated runtime constants
  • ADR 0048: erased type aliases
  • ADR 0049: nominal scalar enums
  • ADR 0050: executable generic specialization
  • architecture/04-intermediate-representations.md
  • architecture/07-implementation-roadmap.md
  • architecture/08.1-closed-design-questions.md
  • architecture/12-type-system-architecture.md
  • architecture/13-syntax-and-nomenclature.md
  • architecture/19-architecture-conformance-and-regression-policy.md
• New or changed public contract:
  • Adds the typed source constructs listed above.
  • Generic calls require explicit type arguments in the bootstrap subset.
  • Generic records use expected-type construction.
  • Reachable generic functions, records, and unions are fully specialized into
    concrete backend-neutral MIR.
  • Arrays remain fixed-length; typed tables may grow deterministically.
  • The experimental C backend remains capability-limited and fail-closed.
  • ROADMAP.md identifies 0.1.0-rc.3 as the current release candidate and
    records the accepted path to 0.1.0.
• Architecture documents, examples, or terminology updated:
  • Updated the IR, type-system, syntax, closed-question, open-question, and
    implementation-roadmap documents.
  • Added ADRs and canonical Luau-shaped examples for the implemented behavior.
  • Preserved Item → Module → Bubble → Package → Workspace terminology.

Verification

• Tests were added or updated before implementation where behavior changed.
• Positive behavior is covered.
• Negative/rejection boundaries are covered.
• Convention, consistency, and regression coverage is present where relevant.
• Cross-backend or differential coverage is present where relevant.
• cargo fmt --all -- --check
• cargo check --workspace --all-targets
• cargo test --workspace --all-targets
• cargo clippy --workspace --all-targets -- -D warnings

If a check was not run, explain why:

• Formatting, workspace checking, and the complete workspace test suite passed
  for the generic implementation before the final compile-time generic test was
  added.
• The current focused test
  explicit_generic_compile_time_calls_use_concrete_static_types fails because
  the compile-time evaluator publishes no constant for the generic call. This
  remains a blocker before merge.
• Focused MIR, driver, interpreter, LLVM, C-backend, and architecture tests
  passed.
• All ROADMAP.md links resolve and git diff --check passed.
• Clippy is blocked by existing warnings in the runtime collector and syntax
  crates, including too_many_lines and Option<Option<T>> warnings.

Review notes

• No dynamic typing, runtime string lookup, broad reflection, or universal-table behavior was introduced.
• HIR/MIR remain backend-neutral.
• No generated artifacts, dependency caches, credentials, or editor files are included.
• This is ready for technical review.

Known limitations and follow-up work:

• Fix the failing explicit generic compile-time constant test before merge.
• The bootstrap generic subset requires explicit type arguments and uses full
  specialization. Type-argument inference, portable generic reference metadata,
  and typed code sharing remain later work.
• The C11 backend remains experimental and rejects unsupported managed/runtime
  behavior instead of providing a fallback.
• Optional narrowing, generalized iteration, typed errors, production GC,
  standard-library completion, Package/Workspace tooling, and final release
  gates are tracked in ROADMAP.md.
• popbook/ is local untracked content and is not included in this pull request.