Release v0.8.0

Update with parser hardening and general improvements toward 100% conformance with the CEL-Spec.

Features

• [#430] Recursion limits and error recovery attempt limit parse-time options
• [#433] Expression size limit parse-time option
• [#443] Change recursion checks to be rule-based, to better match the spec
• [#446] Make it to use a single proto message's fields as the basis for all CEL variables
• [#447] Parser error recovery lookahead limit to prevent pathological backtracking

Fixes

• [#422] Return errors when duration or timestamp overflow is detected
• [#423] Preserve subsecond precision when converting timestamps from strings
• [#427] Use accessor methods for source info instead of fields directly to avoid panic
• [#436] Fix the IsChecked call for constant expressions
• [#439] Ensure RemoveErrorListeners() is called on lexer and parser objects allocated from pools.
• [#448] Unify overflow checking in operators, field setting.
• [#449] Fix list and map equality to preserve logical ANDing of elements

Performance

• [#426] Optimize the antlr.CharStream implementation