perf: hoist regexp.MustCompile calls to package-level vars in validateExpressionForDangerousProps

[Copilot]

validateExpressionForDangerousProps was compiling two constant regex patterns on every call — one at function scope and one inside the for loop — accumulating unnecessary allocations since validateSingleExpression is recursive and runs on every expression in every compiled workflow.

Changes

• pkg/workflow/expression_validation.go: Added exprPartSplitRe and exprNumericPartRe to the existing package-level var block; replaced the inline regexp.MustCompile calls with references to these vars.

// Before
parts := regexp.MustCompile(`[.\[\]]+`).Split(trimmed, -1)
for _, part := range parts {
    if part == "" || regexp.MustCompile(`^\d+$`).MatchString(part) {

// After
parts := exprPartSplitRe.Split(trimmed, -1)
for _, part := range parts {
    if part == "" || exprNumericPartRe.MatchString(part) {

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[Copilot]

Pull request overview

Optimizes expression validation performance by avoiding repeated compilation of constant regular expressions in validateExpressionForDangerousProps, which is invoked frequently during recursive expression validation.

Changes:

• Hoists the expression-splitting regexp into a package-level precompiled variable.
• Hoists the numeric-part-matching regexp into a package-level precompiled variable.
• Updates validateExpressionForDangerousProps to reuse the precompiled regexps.

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[Copilot]

The package-level precompiled regexp vars in this file consistently use the ...Regex suffix (e.g., expressionRegex, needsStepsRegex, numberLiteralRegex). These new names use ...Re, which is inconsistent and makes it harder to scan for regexp vars. Consider renaming to exprPartSplitRegex / exprNumericPartRegex (or another ...Regex-suffixed convention used here).