Improve unary with sign expression handling

[xenova]

fixes {{ 0 in axes or -4 in axes }}

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Note

Medium Risk
Changes expression parsing precedence and unary evaluation across lexer/parser/runtime; behavior shifts for any template using +/- before identifiers or in, though tests lock expected outcomes.

Overview
Fixes templates like {% if 0 in axes or -4 in axes %} by treating leading +/- as unary sign on the following value, not as binary subtraction glued to in.

The parser adds parseUnarySignExpression (used before filters) so expressions such as -4 in axes, -apple | abs, and -(apple + 1) in arr build UnaryExpression nodes. The lexer now folds fractional digits after a unary sign into one numeric token (e.g. -1.5). The runtime evaluates unary +/- on numbers and booleans; float formatting and FloatValue.toString() handle -0.0 and whole-number floats consistently. Coverage is extended via UNARY_SIGN_EXPRESSIONS in templates.test.js.

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