Fix gremlin-go negative BigInteger decoding and P.outside()

[GumpacG]

gremlin-go bug fixes

Two gremlin-go bugs introduced in 4.0.0-beta.2. Both made gremlin-go the only
GLV producing incorrect results; the fixes align it with gremlin-java,
gremlin-python, gremlin-dotnet, and gremlin-javascript.

1. Negative BigInteger / BigDecimal decoded incorrectly

Problem: readBigInt reconstructed negative two's-complement values with a bit
width one byte too wide ((len(b)+1)*8 instead of len(b)*8), so it subtracted a
power of two that was 256x too large. Positive values were unaffected. Negative
BigDecimal values were affected too, because their unscaled value decodes through
the same path. Go was the only GLV with this bug because it hand-rolls the
conversion (math/big has no signed-bytes constructor), while the other GLVs
delegate to a correct standard-library primitive.

Use case: a ledger service stores account balances as arbitrary-precision integers
so they never overflow. Account acct-1 is overdrawn by 500, stored as the
BigInteger -500.

Before:

r, _ := g.V("acct-1").Values("balance").Next()
balance := r.GetInterface() // *big.Int
// want:  -500
// got:   -16712180   (silently wrong, no error returned)

The application reads a balance of -16,712,180 for an account that is only 500
overdrawn. The error is silent, so it can flow into downstream calculations,
alerts, or stored data before anyone notices.

After:

r, _ := g.V("acct-1").Values("balance").Next()
balance := r.GetInterface() // *big.Int
// -500, matching the server and every other GLV

2. P.outside() generated invalid gremlin-lang

Problem: translatePValue list-wrapped the arguments of any multi-value predicate
except between and inside, but outside was omitted from that exclusion.
outside takes exactly two arguments in the grammar (like between/inside), so
they must be comma-separated, not wrapped in a list.

Use case: an anomaly-detection query finds sensor readings outside the normal
operating range of 18 to 65 (too cold or too hot).

Before:

readings, err := g.V().Has("temperature", gremlingo.P.Outside(18, 65)).ToList()
// generated gremlin-lang: g.V().has("temperature",outside([18,65]))
// err: server-side parse error - "outside([18,65])" is not valid gremlin-lang
// readings: nil

The query never runs. Because the identical query works from the Java, Python,
.NET, and JavaScript drivers, the failure looks like a server or environment
problem rather than a driver bug, and P.Outside is effectively unusable from Go.

After:

readings, err := g.V().Has("temperature", gremlingo.P.Outside(18, 65)).ToList()
// generated gremlin-lang: g.V().has("temperature",outside(18,65))
// err: nil
// readings: the out-of-range vertices, as expected

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.46%. Comparing base (a28cd1f) to head (1e8487d).
⚠️ Report is 277 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3522      +/-   ##
============================================
+ Coverage     76.35%   76.46%   +0.10%     
- Complexity    13424    14272     +848     
============================================
  Files          1012     1036      +24     
  Lines         60341    64527    +4186     
  Branches       7075     7650     +575     
============================================
+ Hits          46076    49338    +3262     
- Misses        11548    12097     +549     
- Partials       2717     3092     +375     

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