Replace narrow_for_display workaround with _FmtRange subclass

nab-resolver's error reporter renders constraints via two code paths:
_narrow_positive (which calls narrow_for_display) and direct interpolation
of Incompatibility.constraint_range in the CONSTRAINT-cause path. The
previous narrow_for_display approach only covered the first path, leaving
CONSTRAINT-cause lines with raw (-inf, X) sentinel notation.

_FmtRange overrides __str__ to produce operator-prefixed output and
overrides all Range operators to preserve the subclass through
composition. _constraint_to_range now returns _FmtRange, so every range
we construct formats itself at every render site. narrow_for_display
becomes a one-line fallback that wraps any library-internal Range the
resolver might surface directly.

Author: bbannier

testing/baselines/tests.builtin-spicy-version-error/output

@@ -1,7 +1,7 @@
 ### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
 error: failed to resolve dependencies: because no versions of one/alice/foo <X.X.X | >X.X.X are available
-because one/alice/foo =X.X.X depends on zeek-builtin/spicy-plugin (-inf, X.X.X)
-so one/alice/foo * and not zeek-builtin/spicy-plugin (-inf, X.X.X)
+because one/alice/foo =X.X.X depends on zeek-builtin/spicy-plugin <X.X.X
+so one/alice/foo * and not zeek-builtin/spicy-plugin <X.X.X
 because no versions of zeek-builtin/spicy-plugin <X.X.X are available
 so one/alice/foo *
 because your project depends on one/alice/foo *

testing/baselines/tests.unsatisfied-version-tag-dependency/fail.out

@@ -1,7 +1,7 @@
 ### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
 error: failed to resolve dependencies: because no versions of one/alice/foo <0.0.0 | >0.0.0 are available
-because one/alice/foo =0.0.0 depends on one/alice/bar 1.0.0
-so one/alice/foo * and not one/alice/bar 1.0.0
+because one/alice/foo =0.0.0 depends on one/alice/bar =1.0.0
+so one/alice/foo * and not one/alice/bar =1.0.0
 because no versions of one/alice/bar =1.0.0 are available
 so one/alice/foo *
 because your project depends on one/alice/foo *

zeekpkg/_resolver.py

@@ -19,6 +19,7 @@
 from nab_resolver.ranges import Range
 from nab_resolver.resolver import Resolver, ResolverProvider
 from nab_resolver.types import Incompatibility, RangeProtocol
+from typing_extensions import Self
 
 from ._util import _semver_versions, git_version_tags, is_sha1
 from .package import (
@@ -74,25 +75,25 @@ def _normalize_constraint(spec: str) -> str:
     return spec
 
 
-def _constraint_to_range(constraint: str) -> Range[semver.Version]:
+def _constraint_to_range(constraint: str) -> _FmtRange:
     """Convert a normalized zkg constraint string to a nab-resolver `Range`."""
     if constraint in ("*", ""):
-        return Range.full()
-    result: Range[semver.Version] = Range.full()
+        return _FmtRange(Range.full()._intervals)
+    result: _FmtRange = _FmtRange(Range.full()._intervals)
     clause = semver.SimpleSpec(_normalize_constraint(constraint)).clause
     matchers = list(clause.clauses) if hasattr(clause, "clauses") else [clause]
     for m in matchers:
         v = semver.Version.coerce(str(m.target))
         if m.operator == ">=":
-            result = result & Range.at_least(v)
+            result = result & _FmtRange(Range.at_least(v)._intervals)
         elif m.operator == ">":
-            result = result & Range.greater_than(v)
+            result = result & _FmtRange(Range.greater_than(v)._intervals)
         elif m.operator == "<=":
-            result = result & Range.at_most(v)
+            result = result & _FmtRange(Range.at_most(v)._intervals)
         elif m.operator == "<":
-            result = result & Range.less_than(v)
+            result = result & _FmtRange(Range.less_than(v)._intervals)
         elif m.operator == "==":
-            result = result & Range.singleton(v)
+            result = result & _FmtRange(Range.singleton(v)._intervals)
     return result
 
 
@@ -349,15 +350,7 @@ def narrow_for_display(
         constraint: RangeProtocol[semver.Version],
     ) -> RangeProtocol[semver.Version]:
         r = cast(Range[semver.Version], constraint)
-        display = _fmt_range(r)
-
-        class _Displayed(Range[semver.Version]):
-            __slots__ = ()
-
-            def __str__(self) -> str:
-                return display
-
-        return cast(RangeProtocol[semver.Version], _Displayed(r._intervals))
+        return _FmtRange(r._intervals)
 
 
 def _run_solver(