[BUG] math.round incorrectly uses HALF_EVEN instead of HALF_UP

[rayokota]

Describe the bug
math.round uses HALF_EVEN (banker's rounding) internally, but cel-java's own function declaration, cel-go's reference implementation, and cel-cpp's reference implementation all specify "ties round away from zero". cel-java is the outlier among the three official reference clients; math.round should instead use HALF_UP

To Reproduce
Check which components this affects:

• parser
• checker
• runtime

Sample expression and input that reproduces the issue:

// sample expression string
math.round(42.5) == 42.0 // should be 43.0

Fix is at #1054