feat: add T-SQL rules T001-T004 and FETCH NEXT pagination support - #23

Closes #22.

Adds four T-SQL-specific rules and a small regex tweak so T-SQL
pagination no longer trips the LIMIT-aware warnings.

New rules

• T001 with-nolock (warning). Flags WITH (NOLOCK) table hints.
  Causes dirty reads.
• T002 xp-cmdshell (error). Flags EXEC xp_cmdshell. Shell-exec
  surface that should never appear in application SQL.
• T003 cursor-declaration (warning). Flags DECLARE ... CURSOR.
  Row-by-row processing where set-based SQL usually does better.
• T004 deprecated-outer-join (error). Flags *= and =* old-style
  outer-join syntax. Unsupported in SQL Server 2012 and later. Uses a
  negative lookbehind to avoid matching modern compound-assignment
  expressions like SET @x *= 2.

Regex tweak

W002 missing-limit and W006 orderby-without-limit now match
FETCH\s+(FIRST|NEXT) instead of only FETCH\s+FIRST, so T-SQL's
OFFSET n ROWS FETCH NEXT m ROWS ONLY pagination counts as bounded.

Scope notes

The originally proposed old-style-join rule is already covered by
S001 ImplicitCrossJoin, so dropped to avoid duplicate findings.

Version bump, README rule-count refresh, and .pre-commit-config.yaml
rev update are intentionally left for a release-prep PR so
precommit_rev_matches_tag does not complain about a tag that does
not yet exist.

Tests

18 new tests in tests/test_tsql.py covering each rule's positive
and negative cases, including:

• T001 flags all whitespace variants and case, ignores WITH cte AS.
• T002 flags xp_cmdshell case-insensitively, ignores sp_executesql.
• T003 flags cursor declarations, ignores DECLARE @i INT.
• T004 flags *= and =*, ignores compound assignment, plain
  assignment, and modern JOIN syntax.
• W002 and W006 accept both FETCH FIRST (existing) and
  FETCH NEXT (new) T-SQL pagination.

Full suite: 80 passed, 1 skipped.