fix(types): relax type constraints broken by stripInternal

Two fixes for type declarations that become invalid after @internal
properties are stripped from .d.ts output:

1. Relax SelectWithout generic constraint from K extends keyof T & string
   to K extends string in MySQL, SingleStore, and SQLite select types.
   The keyof T constraint fails when @internal-stripped properties like
   'session' appear in excluded method lists but are absent from the
   emitted type. Omit<> already handles missing keys safely.

2. Remove implements PgPolicyConfig/GelPolicyConfig from PgPolicy/GelPolicy
   class declarations. The optional config properties (as?, for?) are
   declared as non-optional readonly in the class, and @internal properties
   are stripped, making the implements clause invalid. The class remains
   structurally compatible without the clause.

Author: YevheniiKotyrlo

drizzle-orm/src/gel-core/policies.ts

@@ -20,7 +20,7 @@ export interface GelPolicyConfig {
 	withCheck?: SQL;
 }
 
-export class GelPolicy implements GelPolicyConfig {
+export class GelPolicy {
 	static readonly [entityKind]: string = 'GelPolicy';
 
 	readonly as: GelPolicyConfig['as'];

drizzle-orm/src/mysql-core/query-builders/select.types.ts

@@ -243,7 +243,7 @@ export type MySqlSetOperatorExcludedMethods =
 export type MySqlSelectWithout<
 	T extends AnyMySqlSelectQueryBuilder,
 	TDynamic extends boolean,
-	K extends keyof T & string,
+	K extends string,
 	TResetExcluded extends boolean = false,
 > = TDynamic extends true ? T : Omit<
 	MySqlSelectKind<

drizzle-orm/src/pg-core/policies.ts

@@ -20,7 +20,7 @@ export interface PgPolicyConfig {
 	withCheck?: SQL;
 }
 
-export class PgPolicy implements PgPolicyConfig {
+export class PgPolicy {
 	static readonly [entityKind]: string = 'PgPolicy';
 
 	readonly as: PgPolicyConfig['as'];

drizzle-orm/src/singlestore-core/query-builders/select.types.ts

@@ -228,7 +228,7 @@ export type SingleStoreSetOperatorExcludedMethods =
 export type SingleStoreSelectWithout<
 	T extends AnySingleStoreSelectQueryBuilder,
 	TDynamic extends boolean,
-	K extends keyof T & string,
+	K extends string,
 	TResetExcluded extends boolean = false,
 > = TDynamic extends true ? T : Omit<
 	SingleStoreSelectKind<

drizzle-orm/src/sqlite-core/query-builders/select.types.ts

@@ -235,7 +235,7 @@ export type CreateSQLiteSelectFromBuilderMode<
 export type SQLiteSelectWithout<
 	T extends AnySQLiteSelectQueryBuilder,
 	TDynamic extends boolean,
-	K extends keyof T & string,
+	K extends string,
 	TResetExcluded extends boolean = false,
 > = TDynamic extends true ? T : Omit<
 	SQLiteSelectKind<