fix: DependsOnEvaluator mishandles trailing semicolons and JS-wrapped doc.field references

[ankitDhwani]

Problem

DependsOnEvaluator (lib/src/utils/depends_on_evaluator.dart) has two related parsing gaps that cause depends_on / link_filters expressions authored on the Frappe web side to silently fail on mobile.

1. Trailing semicolon breaks value comparison

Some depends_on expressions are authored with a trailing statement terminator, e.g.:

eval:doc.some_checkbox == 1;

_extractValue only matches bare numeric/string literals. The trailing ; survives into the comparison value, so the numeric-literal regex never matches and the expression falls through to a string comparison that never succeeds — the dependent field is permanently hidden regardless of the checkbox's actual state.

2. doc.field reference inside a wrapped JS expression isn't recognized

extractEvalDocField is used for dependent-field detection (the "select X first" UX on Link fields with link_filters). It only matches a bare eval:doc.field value. Real-world link_filters frequently wrap the reference in a JS expression, e.g.:

eval:(doc.category||'').replace(/^prefix\s*/, '')

extractEvalDocField returns null for this — the dependent-field gate never kicks in, and the Link field just resolves zero options with no indication of why, instead of prompting the user to fill in the dependency first.

Expected behaviour

1. _extractValue should strip a trailing ; before attempting numeric/string literal parsing.
2. extractEvalDocField should fall back to a regex search for the first doc.<field> reference anywhere in the expression when the whole expression isn't a bare doc.field value.

Suggested fix

Both fixes are small, additive, and don't change existing passing behavior — see attached PR.