feat(go,types): add FileType, Cardinality, AdjListType

[ZekiLiu]

Reason for this PR

Part of the pure-Go GraphAr SDK (tracking issus #828), following the bootstrap PR #937.
This is the foundational types package: the primitive value enums every higher
layer (info, reader/writer) depends on. Kept separate from DataType (next PR) so
each PR stays a single, reviewable module. The diff is a bit over the usual size,
but about half is table-driven tests and the four enums are one cohesive,
dependency-free unit; splitting them further would fragment the value layer.

What changes are included in this PR?

New package go/graphar/types with four on-disk value types plus their string
parse/serialize and sentinel errors:

• FileType — csv / parquet / orc / json
• Cardinality — single / list / set
• AdjListType — unordered/ordered × by_source/by_dest, with helpers to convert
  to/from the legacy (ordered, aligned_by) form (src/dst)

Enum members and on-disk spellings match the C++ and Java SDKs (verified
member-by-member); Rust and Python are FFI/bindings over C++. No Arrow or
third-party dependency.

Are these changes tested?

Yes. Table-driven unit tests cover round-trips, error paths, defensive copying,
and the lenient/strict version-string cases.

Are there any user-facing changes?

Yes — this adds the public types package. No breaking changes (new code only).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.78%. Comparing base (54601c9) to head (ab8ea0e).

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #941      +/-   ##
============================================
+ Coverage     77.40%   77.78%   +0.37%     
  Complexity      615      615              
============================================
  Files            84       88       +4     
  Lines          8957     9109     +152     
  Branches       1069     1069              
============================================
+ Hits           6933     7085     +152     
  Misses         1784     1784              
  Partials        240      240              

Flag	Coverage Δ
go	100.00% <100.00%> (?)

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