test(spanner): add location router finder golden tests and centralize textproto test utils

[olavloite]

• Add golden conformance test suite for finder_test.textproto (36 test cases, 203 request events) validating query key encoding, range cache lookups, server selection, and routing hints.
• Centralize all golden test fixtures and parsers (recipe_test, cache_test, finder_test) into textproto_test_utils.rs.
• Add unescape_bytes support for hex \xHH sequences and standard C escapes.
• Introduce reusable skip_block helper and decouple nested list value parsing.
• Tighten golden routing hint assertions with strict struct equality, verifying skipped_tablet_uid and per-event unhealthy server isolation matching Java and Go reference implementations.

[gemini-code-assist]

Code Review

This pull request consolidates and refactors the textproto parsing utilities for Spanner golden tests into a shared helper module (textproto_test_utils.rs), removing duplicate parsing code from key_range_cache/golden_tests.rs and key_recipe/golden_tests.rs. It also introduces a new set of golden conformance tests for the location router (location_router/golden_tests.rs). The review feedback suggests improving null value handling in the newly introduced parsing helpers: specifically, adding support for null_value: NULL_VALUE in parse_constant_value and allowing serde_json::Value::Null in query_params_to_target_range to prevent premature termination of key encoding.

[codecov]

Codecov Report

❌ Patch coverage is 97.06411% with 49 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.38%. Comparing base (9ed9339) to head (bc7b235).

Files with missing lines	Patch %	Lines
src/spanner/src/routing/textproto_test_utils.rs	97.06%	49 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             main    #6482     +/-   ##
=========================================
  Coverage   96.37%   96.38%             
=========================================
  Files         297      297             
  Lines       84017    85683   +1666     
=========================================
+ Hits        80971    82584   +1613     
- Misses       3046     3099     +53     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request consolidates textproto parsing logic from multiple golden test files into a shared utility module, textproto_test_utils.rs, while adding support for hex escape sequences and comprehensive unit tests. It also introduces a new golden conformance test suite for the location router. The review feedback highlights opportunities to optimize performance by avoiding unnecessary vector clones in location_router/golden_tests.rs and suggests enhancing parse_constant_value in textproto_test_utils.rs to support parsing float values.

[gemini-code-assist]

The ss_key vector is not used after this point, so cloning it into start is unnecessary. We can avoid the allocation and copy by moving ss_key directly.

Suggested change

	let start = ss_key.clone();
	let start = ss_key;

References

1. Scrutinize expensive uses of clone() and move the data instead if it is not necessary to copy. ^(link)

[gemini-code-assist]

The ss_key vector is not used after this point, so cloning it into start is unnecessary. We can avoid the allocation and copy by moving ss_key directly.

Suggested change

	let start = ss_key.clone();
	let start = ss_key;

References

1. Scrutinize expensive uses of clone() and move the data instead if it is not necessary to copy. ^(link)

[gemini-code-assist]

Currently, parse_constant_value only attempts to parse number_value as an i64. If a float value (e.g., 3.14) is provided as a constant or query parameter in the textproto, parsing will fail and return None. We should support parsing floats as well to ensure robustness and parity with json_to_spanner_value.

pub(crate) fn parse_constant_value(trimmed: &str) -> Option<serde_json::Value> {
    if let Some(string_val) = extract_value(trimmed, "string_value:") {
        Some(serde_json::Value::String(string_val.to_string()))
    } else if let Some(number_val) = extract_value(trimmed, "number_value:") {
        if let Ok(integer) = number_val.parse::<i64>() {
            Some(serde_json::Value::Number(integer.into()))
        } else if let Ok(float) = number_val.parse::<f64>() {
            serde_json::Number::from_f64(float).map(serde_json::Value::Number)
        } else {
            None
        }
    } else {
        extract_value(trimmed, "bool_value:")
            .map(|bool_val| serde_json::Value::Bool(bool_val == "true"))
    }
}