fix(dynamodb): BETWEEN-aware + whitespace-tolerant AND/OR tokenizer

[vieiralucas]

Summary

• The DynamoDB expression splitter used a literal " AND " / " OR " match. That broke for BETWEEN :lo AND :hi (the inner AND got treated as a top-level separator) and for any non-space whitespace between tokens (tabs, newlines, multi-space).
• Rewrite split_on_top_level_keyword around a keyword-boundary helper (match_keyword). Alphanumeric keywords (AND/OR/BETWEEN) now require ASCII-whitespace word boundaries; punctuation keywords (,) still match literally.
• Track a top-level BETWEEN skip counter so x BETWEEN :lo AND :hi no longer has its inner AND consumed as a top-level separator.
• Unignores 3 tests that were parked for this bug:
  • key_condition_between
  • key_condition_whitespace_variations
  • filter_between
• Adds direct unit tests for split_on_top_level_keyword covering BETWEEN skip, whitespace variants, case-insensitive keyword matching, and identifier substrings (e.g. land must not match AND).

Test plan

• cargo test -p fakecloud-dynamodb --lib (all 213 pass, 3 ignored remaining for follow-up PRs)
• cargo test -p fakecloud-e2e --test dynamodb (all 46 pass)
• cargo clippy -p fakecloud-dynamodb --all-targets -- -D warnings
• cargo fmt --all

---

Summary by cubic

Fixes DynamoDB expression splitting so top-level AND/OR no longer break on BETWEEN’s inner AND and tolerate tabs/newlines/multi-space. Re-enables impacted tests and adds targeted unit tests for the tokenizer.

• Bug Fixes
  • Make AND/OR splitting BETWEEN-aware so x BETWEEN :lo AND :hi doesn’t split on the inner AND.
  • Support ASCII whitespace around keywords (tabs, newlines, multiple spaces) and case-insensitive matching.
  • Enforce word boundaries to avoid matching inside identifiers (e.g., land), and respect parentheses.
  • Add match_keyword helper and refactor split_on_top_level_keyword.
  • Unignore key_condition_between, key_condition_whitespace_variations, filter_between; add new tokenizer unit tests.

^{Written for commit 6fbf67a. Summary will update on new commits.}

[codecov]

Codecov Report

❌ Patch coverage is 98.87640% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/fakecloud-dynamodb/src/service/mod.rs	98.87%	1 Missing ⚠️

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[cubic-dev-ai]

No issues found across 2 files