chore: Remove unused imports in normalized_shadow modules

Cleaned up unused imports after Phase 143 execution fix (5e662eaaf).

**Priority files (Phase 143)**:
- if_as_last_join_k.rs: removed ValueId, BTreeMap
- loop_true_break_once.rs: added #[cfg(test)] for test-only imports
- post_if_post_k.rs: removed ValueId, BTreeMap
- normalized_helpers.rs: added #[cfg(test)] for Span

**Additional cleanup**:
- contract_checks.rs: removed BasicBlockId
- joinir/mod.rs: removed Info struct re-exports (functions kept)
- patterns/mod.rs: removed Info struct re-exports (functions kept)
- ast_feature_extractor.rs: removed EscapeSkipPatternInfo
- plan_box.rs: added #[cfg(test)] for PlanKind

**Verification**:
- 0 unused import warnings (was 20+)
- All 69 normalized_shadow tests pass
- Clean build with --release

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/mir/builder/control_flow/joinir/patterns/mod.rs

@@ -84,19 +84,19 @@ pub(in crate::mir::builder) mod trim_pattern_validator;
 pub(in crate::mir::builder) use router::{route_loop_pattern, LoopPatternContext};
 
 // Phase 140-P4-A: Re-export for loop_canonicalizer SSOT (crate-wide visibility)
-pub(crate) use ast_feature_extractor::{detect_skip_whitespace_pattern, SkipWhitespaceInfo};
+pub(crate) use ast_feature_extractor::detect_skip_whitespace_pattern;
 
 // Phase 104: Re-export read_digits(loop(true)) detection for loop_canonicalizer
-pub(crate) use ast_feature_extractor::{detect_read_digits_loop_true_pattern, ReadDigitsLoopTrueInfo};
+pub(crate) use ast_feature_extractor::detect_read_digits_loop_true_pattern;
 
 // Phase 142-P1: Re-export continue pattern detection for loop_canonicalizer
-pub(crate) use ast_feature_extractor::{detect_continue_pattern, ContinuePatternInfo};
+pub(crate) use ast_feature_extractor::detect_continue_pattern;
 
 // Phase 143-P0: Re-export parse_number pattern detection for loop_canonicalizer
-pub(crate) use ast_feature_extractor::{detect_parse_number_pattern, ParseNumberInfo};
+pub(crate) use ast_feature_extractor::detect_parse_number_pattern;
 
 // Phase 143-P1: Re-export parse_string pattern detection for loop_canonicalizer
-pub(crate) use ast_feature_extractor::{detect_parse_string_pattern, ParseStringInfo};
+pub(crate) use ast_feature_extractor::detect_parse_string_pattern;
 
 // Phase 91 P5b: Re-export escape skip pattern detection for loop_canonicalizer
-pub(crate) use ast_feature_extractor::{detect_escape_skip_pattern, EscapeSkipPatternInfo};
+pub(crate) use ast_feature_extractor::detect_escape_skip_pattern;