fix(postgrest): override limit and offset instead of appending duplicates

[AndroidPoet]

What

limit() and range() built their query params with appendSearchParams, which accumulates repeated keys. Because limit and offset are single-valued in PostgREST, chaining or re-applying them emitted duplicate, conflicting params:

from('t').select().limit(5).range(0, 9); // select=*&limit=5&limit=10&offset=0
from('t').select().limit(1).limit(2);     // limit=1&limit=2
from('t').select().range(0, 9).range(10, 19); // offset=0&offset=10&limit=10&limit=10

This overrides those keys so the last call wins.

Why

limit/range used appendSearchParams, but select (postgrest_transform_builder.dart:46) and order (:88) in the same file already use overrideSearchParams for exactly this reason. postgrest-js also uses searchParams.set(...) for limit and range. Emitting two limit/offset values is ambiguous and diverges from both.

Fix: give overrideSearchParams the same optional [Uri? url] parameter that appendSearchParams already has, then use it for limit (single key) and range (both offset and limit).

Not a breaking change

A single limit()/range() call produces the same query string as before — only the previously-duplicated case changes (the last value now wins, which is the documented intent). overrideSearchParams gains an optional parameter, so existing callers are unaffected.

Tests

Added packages/postgrest/test/limit_range_test.dart (URL-capturing mock): .limit(1).limit(2) → limit=2; .limit(5).range(0,9) → single limit=10 + offset=0; .range(0,9).range(10,19) → single offset=10/limit=10; and the referencedTable variant stays scoped and single-valued. All fail on the current code (e.g. Actual: ['1', '2']) and pass with the fix. dart format and dart analyze --fatal-warnings are clean.