v1.10.0

Routes Number.to() through the active UnitSystem, establishing
UnitSystem as the authority for unit resolution and graph lookup. This
is the first step toward retiring module-level global state; all existing
call sites continue to work without changes.

Added

• UnitSystem.resolve_unit(name) — resolves a unit name, alias,
  scale-prefixed name, or composite expression string to a Unit or
  UnitProduct, drawing from the system's unit registry. Delegates to
  parse_unit() with system=self.

• Top-level exports: active(), use() — the active-system
  accessor and context-manager scoping function are now importable
  directly from ucon. active() returns the currently active
  UnitSystem, falling back to UnitSystem.from_globals() when none
  has been set.

• get_default_graph() checks active system — resolution priority
  is now: context-local graph (from using_conversion_graph) →
  active UnitSystem's conversion_graph → module-level default
  (legacy fallback).

• tests/ucon/test_deprecation.py — parametrized test coverage for
  all deprecated symbols emitting DeprecationWarning.

Changed

• Number.to() routes through active() — when neither system=
  nor graph= is provided, Number.to() obtains both the conversion
  graph and unit resolver from the active UnitSystem instead of
  importing get_default_graph and parse_unit directly. Callers see
  no behavioral change; the method signature is unchanged.

• Deprecation warnings upgraded to DeprecationWarning — the
  following symbols previously emitted PendingDeprecationWarning
  (introduced in v1.8) and now emit DeprecationWarning, the standard
  signal that removal is forthcoming in v2.0:

  • UnitSystem.conversions property (use conversion_graph)
  • UnitSystem(conversions=...) constructor kwarg (use conversion_graph=)
  • using_graph() (use using_conversion_graph())
  • set_default_basis_graph() (use with use(system): ...)
  • reset_default_basis_graph() (use with use(system): ...)

Notes

• UnitSystem is not yet exported as the real class from ucon. The
  PEP-562 alias ucon.UnitSystem → BaseUnits remains active with a
  DeprecationWarning. The alias will be retired and UnitSystem
  exported directly in v2.0.

• Module-level globals are still functional. This release wires
  UnitSystem as the routing authority but does not deprecate
  set_default_graph(), reset_default_graph(), or from_globals().
  Those deprecations land in a subsequent v1.x release once test
  infrastructure has migrated to use() scoping.