feat: add java.time.LocalTime converters

[leehaut]

Purpose of the pull request

Related: #1017

Add first-class converter support for java.time.LocalTime, following the existing LocalDate / LocalDateTime pattern.

What's changed?

Excel has no native time-only cell type. This PR treats LocalTime as the time-of-day counterpart of LocalDate:

• Writing preserves the wall-clock time, attaches DateUtils.EPOCH (1970-01-01) as the date component, and applies HH:mm:ss so Excel shows time only.
• Reading drops any date component with toLocalTime(). An Excel-native fraction (0.5 = 12:00:00) and a full datetime serial that happens to be 12:00:00 both become LocalTime.of(12, 0, 0).

Converter family under org.apache.fesod.sheet.converters.localtime:

• LocalTimeDateConverter — default write path (DATE cell, format HH:mm:ss)
• LocalTimeNumberConverter — bidirectional Excel numeric serial, including use1904windowing
• LocalTimeStringConverter — bidirectional STRING cell; default HH:mm:ss, also auto-detects HH:mm, respects @DateTimeFormat and Locale

DateUtils additions (mirroring parseLocalDate / format(LocalDate)):

• DEFAULT_LOCAL_TIME_FORMAT / TIME_FORMAT_8 / TIME_FORMAT_5
• parseLocalTime(...) / format(LocalTime, ...) / switchTimeFormat(...) / getLocalTime(...)

Registration in DefaultConverterLoader matches LocalDateTime:

• Number and String converters in initAllConverter()
• Date converter as the default write converter
• String converter for string-formatted writes

Scope is limited to java.time.LocalTime (JDK 8). Converter lookup is keyed by the declared Java class, so existing Date converters do not cover LocalTime fields.

[bengbengbalabalabeng]

The newly added files in this PR are implemented from scratch and are not derived from Alibaba's EasyExcel. Therefore, no EasyExcel-related license header is required for these files.

Please refer to: https://github.com/apache/fesod/blob/main/fesod-sheet/src/main/java/org/apache/fesod/sheet/FesodSheet.java

[leehaut]

The newly added files in this PR are implemented from scratch and are not derived from Alibaba's EasyExcel. Therefore, no EasyExcel-related license header is required for these files.

Please refer to: https://github.com/apache/fesod/blob/main/fesod-sheet/src/main/java/org/apache/fesod/sheet/FesodSheet.java

Thanks for the catch. Removed the EasyExcel-derived license header from the newly added LocalTime converter files; they now keep the Apache 2.0 header only, consistent with FesodSheet.java.

[Copilot]

Pull request overview

Adds first-class java.time.LocalTime conversion support for Excel date, numeric, and string cells.

Changes:

• Adds LocalTime parsing, formatting, and serial utilities.
• Adds and registers date, number, and string converters.
• Expands test models and converter round-trip coverage.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Summary
fesod-sheet/src/test/java/org/apache/fesod/sheet/util/TestUtil.java	Adds shared LocalTime test fixtures.
fesod-sheet/src/test/java/org/apache/fesod/sheet/util/DateUtilsTest.java	Tests LocalTime utility behavior.
fesod-sheet/src/test/java/org/apache/fesod/sheet/testkit/models/ConverterBaseData.java	Adds LocalTime test-model data.
fesod-sheet/src/test/java/org/apache/fesod/sheet/testkit/builders/TestDataBuilderTest.java	Verifies LocalTime fixture population.
fesod-sheet/src/test/java/org/apache/fesod/sheet/testkit/builders/TestDataBuilder.java	Populates LocalTime test data.
fesod-sheet/src/test/java/org/apache/fesod/sheet/converters/localtime/LocalTimeStringConverterTest.java	Tests string conversion and formats.
fesod-sheet/src/test/java/org/apache/fesod/sheet/converters/localtime/LocalTimeNumberConverterTest.java	Tests numeric conversion and windowing.
fesod-sheet/src/test/java/org/apache/fesod/sheet/converters/localtime/LocalTimeDateConverterTest.java	Tests date-cell conversion.
fesod-sheet/src/test/java/org/apache/fesod/sheet/converters/DefaultConverterLoaderTest.java	Verifies converter registration.
fesod-sheet/src/test/java/org/apache/fesod/sheet/converter/ConverterDataTest.java	Covers converter format round trips.
fesod-sheet/src/main/java/org/apache/fesod/sheet/util/DateUtils.java	Adds LocalTime utilities and formats.
fesod-sheet/src/main/java/org/apache/fesod/sheet/converters/localtime/LocalTimeStringConverter.java	Implements string conversion.
fesod-sheet/src/main/java/org/apache/fesod/sheet/converters/localtime/LocalTimeNumberConverter.java	Implements numeric serial conversion.
fesod-sheet/src/main/java/org/apache/fesod/sheet/converters/localtime/LocalTimeDateConverter.java	Implements date-cell conversion; empty @DateTimeFormat.value() should be normalized to use the HH:mm:ss default.
fesod-sheet/src/main/java/org/apache/fesod/sheet/converters/DefaultConverterLoader.java	Registers the LocalTime converter family.

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[bengbengbalabalabeng]

LGTM.