perf(r8): drop the protobuf and gRPC server keep rules (#1370)

* perf(r8): drop the protobuf and gRPC server keep rules

`-keep class * extends GeneratedMessageLite { *; }` and its $Builder twin pinned
29,633 items — 94% of the app's entire keep radius — and blocked R8 from optimizing
24,909 methods, 81% of every method it was forbidden to touch. Both are replaced by a
field-only rule that now ships inside com.flipcash:{ocp,flipcash2}-client-protocol,
where the generated messages live. javalite resolves fields reflectively and reaches
builders and message methods from ordinary call sites, so the methods never needed
keeping.

`-keep class * implements io.grpc.BindableService { *; }` goes with them. All 45
matches were *ImplBase and *CoroutineImplBase server skeletons generated alongside the
client stubs; nothing in an Android client implements a gRPC service, and no other rule
kept them, so R8 can now delete them outright.

Measured by the R8 configuration analyzer, before and after:

    live methods    230,686 -> 205,144   (-25,542)
    live classes     42,338 ->  41,770      (-568)
    live fields      96,939 ->  95,692    (-1,247)

    obfuscation score  89.0% -> 96.1%
    optimization score 89.3% -> 96.3%
    shrinking score    89.1% -> 96.1%

The AbstractStub rule stays for now. It pins 114 classes with all members and the stubs
are reached from generated newStub() factories, so it is very likely removable too, but
that one needs a run on a device rather than a static argument.

Merges after both contract packages publish the rule; the pinned versions in
libs.versions.toml have to carry it first.

* build(deps): take the contract packages at 0.3.0 for their keep rules

0.3.0 is the first release of either package to ship
META-INF/proguard/*.pro alongside its generated messages, which is what makes
the removal of the app's own protobuf rules in this branch safe. Both jars on
Central carry the rule; R8 reads it straight out of the dependency.

Pinning the version and dropping the local rules in one change keeps the app
from ever sitting on a commit with no protobuf keep rule at all.

Author: bmc08gt

apps/flipcash/app/proguard-rules.pro

@@ -7,15 +7,13 @@
 -keepnames class com.flipcash.app.core.AppRoute
 -keepnames class com.flipcash.app.core.AppRoute$**
 
-# Protobuf — keep all generated message classes and their builders.
-# Using type-hierarchy rules so new packages / updated gRPC stubs are
-# caught automatically instead of listing every gen package.
--keep class * extends com.google.protobuf.GeneratedMessageLite { *; }
--keep class * extends com.google.protobuf.GeneratedMessageLite$Builder { *; }
+# Protobuf keep rules ship with the contract packages themselves, from 0.3.0 on:
+# com.flipcash:{ocp,flipcash2}-client-protocol carry them in META-INF/proguard/, which
+# R8 reads straight out of the jar. Downgrading either pin below 0.3.0 silently removes
+# the app's only protobuf keep rule.
 
-# gRPC — keep generated service stubs (abstract + concrete)
+# gRPC — keep the generated client stubs
 -keep class * extends io.grpc.stub.AbstractStub { *; }
--keep class * implements io.grpc.BindableService { *; }
 
 # Keep our scan classes that interact with native. The scanner's JNI constructs
 # these from C++ by name (FindClass("com/kik/scan/UsernameKikCode"), GetMethodID

gradle/libs.versions.toml

@@ -66,8 +66,10 @@ protovalidate-kt = "0.1.1"
 # Generated client SDKs for the two backend contracts. Separate versions on purpose: the
 # protos are independent (flipcash2 does not import ocp), so the packages move on their own
 # cadence and there is nothing to keep aligned.
-ocp-client-protocol = "0.2.0"
-flipcash2-client-protocol = "0.2.0"
+# 0.3.0 is the first release of either package to ship R8 keep rules for its generated
+# messages, which is what lets proguard-rules.pro drop its own.
+ocp-client-protocol = "0.3.0"
+flipcash2-client-protocol = "0.3.0"
 
 # The Android port is the ONLY libphonenumber this app depends on, deliberately. Google's
 # `com.googlecode` artifact used to sit alongside it; the two ship separate copies of the metadata,